Geology and tectonic evolution of the central-southern Apennines, Italy (GSA Special Paper 469)

Geology and Tectonic Evolution of the Central-Southern Apennines, Italy

by Livio Vezzani Dipartimento di Scienze della Terra Università di Torino Torino, Italy Andrea Festa Dipartimento di Scienze della Terra Università di Torino Torino, Italy and Department of Geology Miami University Oxford, Ohio USA Francesca C. Ghisetti TerraGeoLogica Christchurch New Zealand and Department of Geological Sciences University of Canterbury New Zealand

Special Paper 469 3300 Penrose Place, P.O. Box 9140

Boulder, Colorado 80301-9140 USA

2010

Copyright © 2010, The Geological Society of America (GSA), Inc. All rights reserved. GSA grants permission to individual scientists to make unlimited photocopies of one or more items from this volume for noncommercial purposes advancing science or education, including classroom use. For permission to make photocopies of any item in this volume for other noncommercial, nonprofit purposes, contact The Geological Society of America. Written permission is required from GSA for all other forms of capture or reproduction of any item in the volume including, but not limited to, all types of electronic or digital scanning or other digital or manual transformation of articles or any portion thereof, such as abstracts, into computer-readable and/or transmittable form for personal or corporate use, either noncommercial or commercial, for-profit or otherwise. Send permission requests to GSA Copyright Permissions, 3300 Penrose Place, P.O. Box 9140, Boulder, Colorado 80301-9140, USA. GSA provides this and other forums for the presentation of diverse opinions and positions by scientists worldwide, regardless of their race, citizenship, gender, religion, or political viewpoint. Opinions presented in this publication do not reflect official positions of the Society. Copyright is not claimed on any material prepared wholly by government employees within the scope of their employment. Published by The Geological Society of America, Inc. 3300 Penrose Place, P.O. Box 9140, Boulder, Colorado 80301-9140, USA www.geosociety.org Printed in U.S.A. GSA Books Science Editors: Marion E. Bickford and Donald I. Siegel Library of Congress Cataloging-in-Publication Data Vezzani, Livio, 1934Geology and tectonic evolution of the central-southern Apennines, Italy / by Livio Vezzani, Andrea Festa, and Francesca C. Ghisetti. p. cm. -- (Special paper ; 469) Includes bibliographical references. ISBN 978-0-8137-2469-0 (pbk.) 1. Geology--Italy--Apennines. 2. Geology, Structural--Italy--Apennines. I. Festa, Andrea, 1970- II. Ghisetti, Francesca C., 1954- III. Title. QE272.V49 2010 554.5--dc22 2010014768 Cover: Geology of the central-southern Apennines superposed on the digital elevation model. See Figure 18 and the “Structural Scheme” on the enclosed CD-ROM for legend. Light to dark blue grading in the offshore corresponds with water depths of –100, –200, –1000, –2000 m, respectively.

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Contents Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 The Apenninic Chain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Regional Setting of the Central-Southern Apennines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Lithostratigraphic Units of the Apenninic Thrust-Belt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Pliocene-Pleistocene Foredeep Top-Thrust Basins Inner Domains Sicilide Units Calabride Units Liguride Units Outer Domains Lazio-Abruzzi and Campania-Lucania Units Abruzzi and Umbria-Marche Units Lagonegro-Sannio Units Sannio-Molise Units Outer Abruzzi Unit La Queglia–Colle Madonna–Teramo Unit Maiella and Mount Alpi Units Casoli Unit Apulia Foreland Regional Structural Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Geometry of the Thrust Belt Inner Units Outer Units Foreland First-Order Structures of the Thrust Belt Sequence of Deformation Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Tectonic Phase 1 (Paleogene) Tectonic Phase 2 (Early-Middle Miocene) Tectonic Phase 3 (Late Tortonian–Early Messinian) Tectonic Phase 4 (Late Messinian–Early Pliocene) Tectonic Phase 5 (Early-Middle Pliocene) Tectonic Phase 6 (Late Pliocene–Early Pleistocene) Extensional Faults Superposed onto the Contractional Edifice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Geometry and Structure of the Normal Faults Normal Faults and Seismicity Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 References Cited. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 iii

The Geological Society of America Special Paper 469 2010

Geology and Tectonic Evolution of the Central-Southern Apennines, Italy Livio Vezzani Dipartimento di Scienze della Terra, Università di Torino, Torino, Italy Andrea Festa Dipartimento di Scienze della Terra, Università di Torino, Torino, Italy, and Department of Geology, Miami University, Oxford, Ohio, USA Francesca C. Ghisetti TerraGeoLogica, Christchurch, New Zealand, and Department of Geological Sciences, University of Canterbury, New Zealand

ABSTRACT The Geological-Structural Map of the Central-Southern Apennines (Italy)1 provides entirely revised and original cartography for a large sector of the orogenic belt that stretches along peninsular Italy. New data collected by the authors over the past 20 years, together with field revisions of published data, and available subsurface data are synthesized in two geological map sheets at scale 1:250,000 giving a regional overview of the stratigraphy, geometry, and structure of the Apenninic fold-and-thrust belt. The Apennines comprise a variety of lithotectonic assemblages that evolved through interaction between the African and European plates in the central Mediterranean, with: (i) Mesozoic development of the Tethyan domain; (ii) CretaceousEocene oceanic subduction; (iii) Oligocene-Miocene and Pliocene convergence, continental collision and shortening; and (iv) late Miocene–present extensional collapse of the contractional edifice. The geological maps and this paper illustrate a number of critical orogenic processes, including: (1) control of paleogeographic position and stratigraphy on the finite geometry of the thrust belt; (2) the history of progressive deformation and translation of far-traveled tectonic units; (3) selective reactivation of inherited structures during the sequence of superposed tectonic events; (4) the evolution of syntectonic and posttectonic sedimentary basins; and, (5) the propagation paths of thrust faults. The paper, together with the geological map and cross sections, provide a regional overview of the progressive tectono-stratigraphic evolution of the thrust belt, with focus on the geometry of the imbricate wedge and its subsurface geometry. Emphasis is also given to the relationships between active faulting and historical seismicity.

1 The Geological-Structural Map of the Central-Southern Apennines (Italy), Sheets 1 and 2, is on a CD-ROM accompanying this volume. The map is also available as GSA Data Repository item 2010136, online at www.geosociety.org/pubs/ft2010.htm, or on request from [email protected], Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301, USA.

Vezzani, L., Festa, A., and Ghisetti, F.C., 2010, Geology and Tectonic Evolution of the Central-Southern Apennines, Italy: Geological Society of America Special Paper 469, 58 p., doi: 10.1130/2010.2469. For permission to copy, contact [email protected]. ©2010 The Geological Society of America. All rights reserved.

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INTRODUCTION The Geological-Structural Map of the Central-Southern Apennines (Italy), scale 1:250,000 (see footnote 1 and Fig. 1 for the location of the area mapped in Sheets 1 and 2) covers the area of 42 topographic sheets at scale of 1:100,000 (Istituto Geografico Militare Italiano, Florence). The map shows the geology of the central-southern Apennines in the administrative regions of Abruzzi, Lazio, Molise, Campania, Puglia, Basilicata and Calabria (see Figure 1 and Plates 1 and 2 for the location of the regions and cited localities). This geological map is the final outcome of a long-term project focused on regional and structural geology of the Italian Apennines, led by a research group from the Earth Sciences Departments of Torino and Catania Universities, Italy. Progressive acquisition and interpretation of new data have been documented in scientific papers (see References Cited), in detailed geological maps at scales of 1:15,000, 1:25,000, and 1:50,000 (see “Cartographic References” in Sheet 2), as well as in geological maps that provide a regional synthesis of the Apennines in the regions of Abruzzi (Vezzani and Ghisetti, 1998) and Molise (Vezzani et al., 2004). Final assemblage of the Geological-Structural Map of the Central-Southern Apennines (Italy) has involved field revisions during 2004–2008 of the authors’ own cartographic data (both published and unpublished), acquisition of new data for improved biostratigraphical, sedimentological, and structural resolution, and the revision and integration of the geological maps listed in the “Cartographic References” in Sheet 2: Crostella and Vezzani (1964), Ogniben (1969), Scandone (1971), Cocco et al. (1974), Lentini (1980), Bigi et al. (1983), Accordi and Carbone (1986), Bonardi et al. (1988b), Ciaranfi et al. (1988), Carbone et al. (1991), Monaco and Tortorici (1994), Bonini and Sani (1999), Matano and Pinto (2000), Selli (2003), APAT (2005), and Patacca and Scandone (2006). Tectonic units distinguished in the Geological Map (Sheets 1 and 2) are separated by major thrust faults and described in the legend (on Sheet 1) in order of tectonic superposition, from top to bottom. Particular care has been devoted to simplifying the complex stratigraphic nomenclature of the lithostratigraphic units, inherited from the traditional use of informal stratigraphic terms and from terminological incongruities introduced over the years by different research groups. Included in the maps are: the structural scheme (on Sheet 2), ten cross sections (on Sheet 2), and a reconstruction of the buried structure of the central-southern Apennines (on Sheet 1, hereafter indicated as BSCSA), based on available seismic and drilling data from oil exploration (Nicolai and Gambini, 2007). This paper focuses on the description of the complex tectonostratigraphic setting of the central-southern Apennines and on defining of their history of progressive, polyphase tectonic evolution, starting from the control exerted by the inherited Mesozoic paleogeographic setting to the Oligo-Miocene and Pliocene convergence and shortening episodes and, finally, to

the late Pliocene–present extensional collapse of the thrust belt. Accompanying figures provide further geological and structural details that contribute to regional interpretation, and photographs illustrate some of the key field relationships in the morphotectonic landscape of the Apennines. THE APENNINIC CHAIN The sinuous mountain chain of the Apennines is one of the several, interconnected, circum-Mediterranean orogens resulting from the late Mesozoic–Cenozoic Alpine orogeny, that preserve the tectonostratigraphic imprints of superposed events of rifting, drifting, subduction, and collision (e.g., Cavazza et al., 2004; Dilek, 2006). This fold-and-thrust belt extends from peninsular Italy to Sicily for a length for ~1500 km, linking the western Alps to the Maghrebian chain of north Africa (Fig. 1). The thrust belt can be subdivided into the arcuate segments of the northern and southern Apennines (see Vai and Martini, 2001; Cavazza et al., 2004; Patacca and Scandone, 2007a), with the intermediate pivot segment of the central Apennines (Ghisetti and Vezzani, 1997; Patacca and Scandone, 2007a), bounded by the Ancona-Anzio Line to the NW (redefined by Salvini and Vittori, 1982, as the Antrodoco–Posta–Mount Sibillini Line), and the Volturno-Sangro Line (or Ortona-Roccamonfina Line of Locardi, 1982) to the SE (Ghisetti and Vezzani, 1983, 1991). The northern Apennines consist of a regular, in-sequence system of N- and NE-verging thrust imbricates. In contrast, the ENE- and E-verging southern Apennines are characterized by duplex geometries and out-of-sequence thrusting (Cavazza et al., 2004). The Central Apennines display N-verging (Gran Sasso, Meta, Matese), and NE- to ENE-verging (Maiella, Mount Morrone, Mount Sirente, Mount Genzana) thrust faults that dissect the tectonic edifice into several, small-scale tectonic slices (Ghisetti and Vezzani, 1997). The present structure of the Apennines results from the interaction between the African plate (Adriatic-Apulia Foreland) and the European plate (Corsica-Sardinia Foreland), with (1) Late Permian to Jurassic and Early Cretaceous rifting, transtension and drifting of the Tethyan margin, accompanied by the opening of the Ligurian-Piedmont ocean; and (2) Late Cretaceous– Cenozoic westward subduction of the Adriatic-Apulia plate, resulting in the progressive shortening and eastward telescoping of the European margin, as well as of the oceanic domains and of the inner margin of the Adriatic-Apulia plate (Bally et al., 1986; Bernoulli, 2001; Cavazza and Wezel, 2003; Elter et al., 2003; Patacca and Scandone, 2007a). Controversy continues as to whether the Apulia Foreland (Adria) was an indenter of the African plate (the “African promontory” of Argand, 1924; see also Dercourt, 1972; Channell et al., 1979; Mele, 2001) or was rather an independent microplate separated from the African plate either by oceanic crust of poorly defined age (e.g., Dewey et al., 1973; Biju-Duval et al., 1977; Dercourt et al., 1986, de Voogd et al., 1992; Catalano et al., 2001) or by stretched continental crust (Panza et al., 2003).

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Figure 1. Structural scheme of Italy and surrounding regions. The two rectangles frame the regions mapped in the Sheets 1 and 2 of the Geological-Structural Map of the Central-Southern Apennines.

Plate 1. Geographic sketch map of Sheet 1 showing localities cited in the text (see footnote 1).

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Plate 2. Geographic sketch map of Sheet 2 showing localities cited in the text (see footnote 1).

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Some recent paleogeographic reconstructions (Ciarapica and Passeri, 2002) envisage two suborthogonal rifting systems guiding the Late Triassic to Early Jurassic separation and passive margin evolution of the Apulia Foreland: the NE-SW Ligurian ocean (Northern Tethyan system), and the NW-SE or WNW-ESE Lagonegro basin (Southern Tethyan system) (Bernoulli, 2001; Ciarapica and Passeri, 2002; Bosellini, 2004). During the Early to Middle Jurassic, continued subsidence following extension led to the progressive drowning of the continental margin. After the Middle Jurassic pelagic sedimentation prevailed over most of the subsiding margin (Bernoulli, 2001; Bosellini, 2004). The accretionary wedge of the Ligurian Units, which represents the most internal paleogeographic domain deposited within the Ligurian oceanic basin (Fig. 2) documents a change in the Africa-Europe plate motion, with Cretaceous to Middle Eocene convergence and onset of oceanic (“B” type) subduction (Marroni et al., 2001; Bortolotti et al., 2005). Orogenic contraction, related to upper Eocene–Oligocene and Miocene continental collision, continued until the late Pliocene with folding and imbrication of the cover succession

detached from its crystalline basement, and large-scale thrusting of the structural units. Progression of shortening is well documented by the onset, development, and uplift of migrating foredeep basins and of top-thrust syncompressional basins, as well as by the progressive westward flexure and shortening of the Apulia Foreland (Selli, 1957, 1962; Ogniben, 1969; D’Argenio et al., 1975; Casero et al., 1988; Patacca and Scandone, 1989; Carbone and Lentini, 1990; Patacca et al., 1992a, 1992b; Cipollari and Cosentino, 1995; Cipollari et al., 1995). From the late Miocene, eastward migration of the orogenic front and of the foredeep-foreland system was accompanied by synchronous extensional collapse of the inner domains of the thrust belt. This process culminated in the crustal thinning and foundering of the Tyrrhenian basin (Fig. 1), interpreted by several authors (e.g., Malinverno and Ryan, 1986; Channell and Mareschal, 1989; Patacca et al., 1990, 1993; Patacca and Scandone, 2004, and references therein) as a back-arc basin behind the retreating Apulia-Adriatic slab. Superposition of upper Pliocene to Pleistocene normal faults onto the compressional fabric of the thrust belt is widespread and controls the intense seismicity of the Apenninic chain (Anderson

Figure 2. Restoration (superposed onto the present coastline) of the paleogeography of the central-southern Apennines after the eo-mesoAlpine deformation of the Liguride and Calabride domains (Paleogene). Note the distribution of carbonate platforms and intervening pelagic basins, from which derive the major tectonic units of the Apenninic thrust belt (see legend of the Geological Map in Sheet 1).

Geology and Tectonic Evolution of the Central-Southern Apennines, Italy and Jackson, 1987; Giardini and Velonà, 1991; Galadini et al., 2000; Ghisetti and Vezzani, 2002b; Barchi et al., 2007). Collapse of the inner domains of the thrust belt led to widespread foundering of the European crust, which is now exposed (Fig. 1) only in the Corsica-Sardinia Foreland and in the Alpine units accreted above the African-Adriatic-Apulia margin (Sartori, 2003). The latter are preserved in the crystalline massifs of Aspromonte, Serre and Sila in Calabria and at Timpa Rotalupo in Basilicata (see Sheet 2), as well as in northeast Sicily (Peloritani Mountains). At present, convergence between the African and European plates occurs at low rates (<1 mm/yr) and in a N-S direction (Ferranti and Oldow, 2005; Corti et al., 2006), but westward subduction of the Adriatic continental lithosphere in the central Apen-

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nines and of a residual slab of Ionian oceanic lithosphere in the Calabrian arc are still active, as documented by seismic tomography, the distribution of deep earthquakes, and volcanism (Rossi and Sartori, 1981; Selvaggi and Chiarabba, 1995; Cernobori et al., 1996; Amato and Cimini, 2001). REGIONAL SETTING OF THE CENTRAL-SOUTHERN APENNINES Major structural domains recognized in central-southern Apennines of Italy (Fig. 3), are (from west to east): (1) The extensional Tyrrhenian and peri-Tyrrhenian domain, with thinned to partly oceanic crust (south of latitude 41° N).

Figure 3. Major crustal and structural domains of the Apennines. The inner domains (west of the orographic divide) are characterized by intense extensional dissection of the thrust belt, with foundering of the Tyrrhenian basin and peri-Tyrrhenian margin, to the WSW of the outer front of crustal stretching. The outermost domains (east of the orographic divide) preserve the contractional features of the thrust belt and display strong components of uplift. Note the axis of the foreland peripheral bulge and the relevant flexure of the Adriatic-Apulia Foreland underneath the outer thrust front of the Apenninic chain, shown by the contours to the top of buried Mesozoic-Tertiary carbonates. The rectangles frame the areas mapped in Sheets 1 and 2 of the Geological-Structural Map of the Central-Southern Apennines.

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The thinned crust overlies a concave and distorted W-dipping Benioff zone (Fig. 1) dipping 50° WNW in the depth interval 250–340 km (where the largest number of strong earthquakes occur), and continuing at a lower angle down to 500 km (Ghisetti et al., 1982; Anderson and Jackson, 1987; Giardini and Velonà, 1991). The peri-Tyrrhenian margin hosts several PliocenePleistocene active volcanic edifices, and is strongly dissected by normal faults that control the evolution of narrow N-S–trending Pliocene-Pleistocene basins (e.g., Gioia and Paola basins), the continental platform and the present coastline. This area is only partially covered by our map. (2) The extensionally downfaulted inner thrust belt is composed of a thick pile of inner thrust sheets (Calabride, Liguride, and Sicilide Units), transported with NE vergence onto the outer Apenninic fold-and-thrust belt, comprising the LazioAbruzzi and Campania-Lucania, Abruzzi and Umbria-Marche, Lagonegro-Sannio, and Sannio-Molise Units (Fig. 4). The whole imbricate stack, 7–8 km thick, tectonically overlies the AdriaticApulia Foreland and its flexural foredeep (Adriatic-Bradanic Foredeep, Fig. 3). The outer Apenninic fold-and-thrust belt exhibits duplex structure, with an upper emergent thrust belt and a lower, buried foreland fold-and-thrust belt consisting of the Apulia-Adriatic deformed Units (Mostardini and Merlini, 1986; Cello et al., 1989; Ghisetti et al., 1993a, 1994; Lentini et al., 1996; Vezzani and Ghisetti, 1998; Menardi Noguera and Rea, 2000; Patacca and Scandone, 2004). (3) The Adriatic-Bradanic Foredeep, developed above the continental margin of the Adriatic-Apulia Foreland (Fig. 3). This is the outermost and youngest flexural basin formed during the Pliocene and Pleistocene, in response to crustal thickening and eastern migration of the orogenic wedge (Jaboli and Roger, 1952; Casnedi et al., 1981; Royden and Karner, 1984; Royden et al. 1987; Sella et al., 1988; Argnani et al., 1991; De Alteriis, 1995). Subsurface data show that the western margin of the foredeep and its western depocentral area are overridden by the allochthonous thrust sheets, with detachment of a thin-skinned external nappe (Metaponto Nappe, Ogniben, 1969). The deformed units are onlapped by upper Pliocene–lower Pleistocene clastic deposits. (4) The Adriatic-Apulia Foreland, emergent in the Gargano and Murge promontories (Figs. 1 and 3). Systems of W-dipping normal faults caused progressive downstepping of the foreland below the thrust belt. The Adriatic-Apulia carbonate substratum beneath the Metaponto Nappe was moderately shortened by compressional inversion of inherited normal faults, and, farther to the west, these buried carbonates are deformed in a foreland fold-and-thrust belt (Pieri, 1966; Bally et al., 1986; Mostardini and Merlini, 1986; Casero et al., 1988; Carbone and Lentini, 1990; Patacca et al., 1992b; Ghisetti et al., 1993a, 1994; Lentini et al., 1996; Vezzani and Ghisetti, 1998; Patacca and Scandone, 2006, 2007a; Nicolai and Gambini, 2007). This buried thrust belt (BSCSA in Sheet 1) is imaged by several seismic reflection lines tied to oil exploration wells, and emerges in the tectonic windows of Casoli, Maiella and Mount Alpi (see cross sections 2 and 9 in Sheet 2).

LITHOSTRATIGRAPHIC UNITS OF THE APENNINIC THRUST-BELT The external successions involved in the thrust belt of the central-southern Apennines were originally deposited in domains of carbonate platforms and interposed pelagic basins along the Adriatic-Apulia-African passive margin (Fig. 2). These thrust sheets are tectonically overlain by internal units, originally deposited above the Tethyan oceanic crust (Liguride Units) and above the thinned continental crust (Sicilide Units) of the Adriatic-Apulia microplate. A summary description of the mapped lithostratigraphic units (lithology, thickness and age) is provided in the legend of the Geological-Structural Map (in Sheet 1) with, from top to bottom: (a) postorogenic marine, terrestrial and volcanic formations of Pliocene-Pleistocene and Holocene age, deposited in intramontane basins (color key 1), and in the Adriatic-Bradanic Foredeep basin along the Adriatic-Ionian coast of the Italian peninsula (color key 2); (b) successions of the syncompressional topthrust basins, deposited during the progressive eastward propagation of shortening (color key 3); (c) lithostratigraphic successions pertaining to different units (color keys from 4 to 14) deformed in the allochthonous thrust sheets of the orogenic wedge, from the uppermost internal domains (Sicilide, Calabride and Liguride Units, color keys 4, 5, and 6, respectively) to the lowermost external domains (from the Lazio-Abruzzi Units, color key 7 to the Casoli Unit, color key 14); (d) Apulia Foreland (color key 15). Pliocene-Pleistocene Foredeep The upper Pliocene–lower Pleistocene deposits of the Adriatic-Bradanic Foredeep are exposed along the east coast of Italy, from the central regions of Marche and Abruzzi in the north, to the Basilicata-Calabria border in the south, and are locally covered by a succession of upper Pleistocene–Holocene terrestrial and marine terraces, recent river deposits, coastal plain alluvium and beach deposits (Vezzani, 1967a). To the east, the transgressive-regressive Pliocene-Pleistocene succession unconformably onlaps the carbonate ramp of the Apulia Foreland (see cross sections 4, 5, and 7 in Sheet 2), and fills major intra-Apenninic tectonic depressions (e.g., San Arcangelo basin, see cross sections 8, 9, and 10 in Sheet 2). To the west, it overlies discordantly the allochthonous thrust sheets, and/or the deposits of the top-thrust basins (e.g., cross sections 1, 2, 3, and 10 in Sheet 2). The foredeep succession starts with basal conglomerates (Turrivalignani conglomerates, 2c), followed upward by the upper Pliocene bluish shelf claystones of the Mutignano Formation (2a). The latter grade laterally and upward to lower Pleistocene shallow-water yellow sandstones (Sands of Serracapriola, 2s), overlain by fluvio-deltaic, littoral deposits and terrestrial conglomerates (Campomarino Conglomerates, 2sc). In the San Arcangelo Basin (Basilicata), the upper Pliocene blue claystones of the Mutignano Formation (2a) grade upward

Figure 4. (A) Stratigraphic and structural relationships between the tectonic units of the central-southern Apennines. (B) Inset illustrating the different geometry of the imbricates in the Abruzzi and Molise regions (central Apennines). Numbers are the same as in the legend of the Geological Map (Sheet 1).

A

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and laterally to the Aliano sands (2s) that consist of prevailing thick beds of yellow sands with conglomeratic lenses of late Pliocene–early Pleistocene age (see Lentini and Vezzani, 1973; Patacca and Scandone, 2001, 2004). These deposits grade upward to the alluvial Castronuovo conglomerates (Vezzani, 1967c), unconformably overlain by the reddish alluvial Sands and Conglomerates of Serra Corneta (2cs) of the early Pleistocene age (Vezzani, 1967c). Top-Thrust Basins These marine sedimentary units were deposited on top of the Apenninic thrust sheets during their displacement toward the Apulia foreland, and progressively incorporated into the Apenninic chain (piggyback basins in Ori and Friend, 1984, thrustsheet-top deposits in Patacca and Scandone, 2007a). These deposits record subsequent steps in the eastward migration of the thrust belt-foredeep system, connected with increasing shortening in the chain, and flexuring of the foreland (Cipollari and Cosentino, 1995; Ghisetti and Vezzani, 1998). The distribution of these lithostratigraphic units that fill topthrust basins of progressively younger age from SW (Albidona Formation, 3fa in Fig. 4) to NE (Atessa Formation, 3aa in Fig. 4) is presented in Figure 5. The Albidona Formation (3fa) crops out in southern Basilicata, in the Mount Pollino area, to the east of Mount Alpi and to the north of Mount Raparo (Plate 2). This succession, up to 2200 m thick, was unconformably deposited above the Liguride Units. The formation consists of alternating silty marls (in beds up to 10 m thick), sandstones with thick beds of calcareous marls, and poorly sorted paraconglomerates with angular to rounded pebbles in a prevailing sandy matrix. The clasts were derived from the underlying Liguride Units (Frido, Crete Nere, and Saraceno Formations), as well as from the Calabride crystalline basement (Vezzani, 1966, 1970). The age of this formation is still debated: it is early-middle Eocene according to Pavan and Pirini (1963), Mostardini et al. (1966), Vezzani (1966, 1970), Ogniben (1969), and Baruffini et al. (2000); late Oligocene–early Burdigalian according to Zuppetta et al. (1984); and Miocene according to Selli (1962), Bonardi et al. (1985), Lentini et al. (1987), and Russo et al. (1995). In our interpretation, the Albidona Formation was deposited in a top-thrust basin that seals the eo-mesoalpine compressional structures of the Cretaceous-Paleogene Liguride and Calabride thrust belt (see Fig. 4). The Gorgoglione Formation (3ea) of Tortonian-SerravallianLanghian (?) age, is the infilling of a later top-thrust basin that unconformably overlies the Sicilide Units (Fig. 6). It consists of a turbiditic succession (up to 1500 m thick), with sandstones, claystones, and subordinate channelled polygenic conglomerates (Selli, 1962; Boenzi and Ciaranfi, 1970; Pescatore and Senatore, 1986; Boiano, 1997). This formation is attributed—together with the Perosa and Oriolo Formations—to a top-thrust basin that seals the contractional

deformation of the Sicilide, Liguride, Lagonegro-Sannio, and Campania-Lucania Units. The two top-thrust basins of the Albidona and Gorgoglione Formations (3fa and 3ea) are probably relatable to the early Eocene to Serravallian semi-allochthonous deposits of the EpiLigurian Units of the northern Apennines (Ricci Lucchi, 1986). The lower Pleistocene to upper Miocene successions that fill the youngest top-thrust basins—from the older Sandstones of Valli (3ds) to the Atessa Formation (3aa)—were unconformably deposited onto the outer domains of the Lazio-Abruzzi and Sannio-Molise Units, during and after their shortening (Ghisetti et al., 1994; Ghisetti and Vezzani, 1986a, 1986b; 1997; Patacca and Scandone, 2004; Festa et al., 2006). The degree of allochthony decreases from the older to the younger top-thrust basins; in some cases (e.g., Castilenti Formation, 3ba, and Atessa Formation, 3aa) there are clear lateral stratigraphic links with the lower Pleistocene–upper Pliocene deposits of the Adriatic-Bradanic Foredeep (Mutignano Formation, 2a). Though the stratigraphic successions of the top-thrust basins are largely allochthonous, the youngest successions that were deposited during thrusting over the autochthonous, external domains of the Adriatic-Apulia Foreland are in fact semiallochthonous or “neo-autochthonous” (Barchi et al., 2001). Overall, the geometric position and evolution of the top-thrust basins provides valuable constraints for the chronological definition of progressive imbrication of the thrusted units (see “Sequence of Deformation Events” section). Inner Domains Sicilide Units The Sicilide Units (Complesso Sicilide of Ogniben, 1960, 1969) were originally deposited in a Tethys-facing basin along the African passive margin (Fig. 2). The nature of their basement (thinned continental crust or oceanic crust) is unknown. Typically, the bulk of the Sicilide Units are Upper Cretaceous–lower Miocene strongly varicolored clays, with heterogeneous and chaotic fabric resulting from poly-phased imbrications. Together with the underlying Calabride and Liguride Units, the Sicilide Units are the topmost thrust sheets of the Apenninic chain (see “Structural Scheme” and cross sections 3, 5, 7, and 10 in Sheet 2), and overlie the whole stack of the more external units (Lazio-Abruzzi and Campania-Lucania, Lagonegro-Sannio and Sannio-Molise). The Sicilide Units tectonically lie above the top-thrust basin of the Albidona Formation (3fa) that seals the Liguride accretionary prism. The tectonic superposition of the Sicilide Units onto the Albidona Formation occurs along a NW-SE, curved thrust fault, in outcrop from Torre Albidona (at the mouth of the Avena River) to Nocara (Plate 2), and accompanied by several small klippen (Ferro River, southeastern corner of Sheet 2 close to the Ionian Sea). The lowermost Sicilide beds crop out close to Nocara at the Calabria-Basilicata border (southern part of Sheet 2; see also Plate 2), with alternating of lithic arkosic sandstones and

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Figure 5. Distribution of the top-thrust basins in the mapped area. Numbers are the same as in the legend of the Geological Map (Sheet 1). The inferred areal extent of top-thrust basins is contoured by gray lines. Note that the eastward younging of the clastic successions infilling the basins constrains the progressive migration of shortening toward the Adriatic-Apulia Foreland (see text for a discussion).

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pelites (300 m thick) passing upward to alternating sandstones and conglomerates with granitic, metamorphic, and calcareous elements (Nocara Flysch of Ogniben, 1969; see also Mostardini et al., 1966) of middle Cretaceous age (Fig. 6). This outcrop is too small to be displayed in the 1:250,000 geological map. This stratigraphic interval is tectonically overlain by the Upper Cretaceous–lower Miocene Varicolored Scaly Clays (“Argille variegate” or “Argille varicolori” of the Italian authors) that consist of thinly bedded red, green, and bluish clays alternating with thin beds of greenish-gray calcilutites, calcarenites, cherty limestones, quartzarenites, and manganesiferous black limestones (Fig. 7). This varicolored clayey succession is stratigraphically overlain by hemipelagic and clastic resedimented limestones with interbedded red marls that show different degrees of strata disruption. Tectonically mixed rocks in which the original stratigraphic succession is highly deformed but still preserved (broken formations) are recognized at the base of the unit and/

or along localized and well-defined horizons of detachment (e.g., the base of the Mount Moschiaturo klippe or the Mount Sant’Arcangelo Formation, see below). Elsewhere the unit consists of chaotic bodies of mixed rocks with a block-in-matrix random arrangement. These represent olistostromes related to masswasting processes (e.g., precursory olistostromes interbedded in the foredeep successions as in the case of the upper Tortonian Frosinone Flysch or the Messinian–upper Tortonian Pietraroja Flysch, see Cipollari and Cosentino, 1995; Festa et al., 2006, 2010a, 2010b). This chaotic setting is largely due to the interplay and partial superposition of tectonic and sedimentary (gravitative) processes (Festa et al., 2010b). These chaotic bodies, including both the broken formations and the olistostromes, are commonly characterized by a mesoscopic scaly texture which is at the origin of the name (Scaly Clays) “Argille Scagliose” (Bianconi, 1840). The total thickness of the Varicolored Scaly Clays amounts to 2000–2500 m. Interlayered in the thick body of varicolored

Figure 6. Inner domains: major tectono-sedimentary characteristics of the Liguride (6) and Sicilide (4) Units and of the Albidona (3fa) and Gorgoglione (3ea) top-thrust basins, cropping out at the boundary between Basilicata and Calabria.

Geology and Tectonic Evolution of the Central-Southern Apennines, Italy pelites is the Mount Sant’Arcangelo Formation, consisting of fine-grained, thin-bedded white limestones alternating with variegated clays and subordinate calcarenites and calcirudites of Upper Cretaceous to lower Eocene age (Ogniben, 1969). The Varicolored Scaly Clays stratigraphically grade upward to an alternance of micritic limestones, marls and green tuffites (early Miocene–Oligocene?), 300–350 m thick. This formation shows strong affinity with the Tusa Tuffites of Sicily (Ogniben, 1960), and with the arenites and conglomerates with andesitic clasts of Petrignacola of the northern Apennines (Elter et al., 1964). These tuffites, probably connected with Alpine subduction (Elter et al., 2003), have been correlated with the Taveyannaz turbiditic succession of the Tertiary North Helvetic Flysch of eastern Switzerland (Ogniben, 1964). As already described in the previous section (see also Fig. 4) the Sicilide Units are covered unconformably by the TortonianSerravallian-Langhian Gorgoglione Formation (see the large outcrops of 3ea above 4av to the north of Corleto Perticara on the left bank of the Sauro River, southern part of Sheet 2). Further south (from Viggiano to San Chirico Raparo, see Plate 2), the Gorgoglione succession (3ea) transgressively covers the Albidona Formation (3fa), the latter sealing unconformably the Liguride Units (see next section). The stratigraphic relationships described so far imply an early translation of the Sicilide Units above the Liguride Units after deposition of the top-thrust Albidona Formation (i.e., at the end of the early Miocene), followed by sedimentation of the Gorgoglione succession at the beginning of middle Miocene (Langhian-Serravallian). In the early stages of the late Miocene (Tortonian) the Liguride and Sicilide Units sealed by the Gorgoglione top-thrust basin overrode the outermost units of the Apenninic edifice (LazioAbruzzi and Campania-Lucania Units, Lagonegro-Sannio Units, and Sannio-Molise Units). In the outermost areas of the Apenninic chain, at the front of the sedimentary accretionary wedge, the Varicolored Scaly Clays of the Sicilide Units define a 10–15 km wide tectono-sedimentary

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mélange (Frentani Tectonic Mélange of Vezzani, Ghisetti, and Festa, 2004; Festa et al., 2006, 2010a, 2010b; Torrente Calaggio Formation of Patacca and Scandone, 2006; Metaponto nappe of Ogniben, 1969). This mélange incorporates the outermost and deepest thrust sheets of the Sannio-Molise Units and it is tectonically interleaved with blocks of Messinian evaporites (3dg) and early-middle Pliocene calcarenites (3cc) and clays (3ca) of the top-thrust basin successions, ranging in size from decimeters to hundreds of meters (Ghisetti et al., 2003; Vezzani et al., 2004; Festa et al., 2006, 2010a, 2010b). The matrix of the Varicolored Scaly Clays is commonly brecciated, with locally developed scaly fabric. The internal geometry of the mélange is consistent with mass-gravity deposits (slope and debris avalanches) produced at the outer frontal thrust of the Apenninic chain during its eastward tectonic migration, overprinted by later tectonic deformation (Ghisetti et al., 2003; Festa et al., 2010a, 2010b). In the central-southern Apennines, the Sicilide Units are thrust over: (1) the external Apulia-Adriatic fold-and-thrust belt, emerging in the tectonic windows of Maiella and Casoli; (2) the Sannio-Molise Units outcropping in the tectonic windows of Vallone Grande and Lucito along the Biferno River (southern part of Sheet 1; see Plate 1); (3) the Lagonegro-Sannio Units (e.g., cross section 5 to the north of San Fele in Sheet 2); (4) the carbonate platform of the Lazio-Abruzzi and Campania-Lucania Units, with precursory olistostromes of Sicilide provenance embedded in the foredeep through mechanisms of mass-wasting at the front of the thrust belt, as documented for the Frosinone Flysch (Cipollari and Cosentino, 1995) and the Pietraroja Flysch (Festa et al., 2006, 2010a, 2010b); (5) the upper Miocene top-thrust basin of the Sandstones of Valli (e.g., south of Lago di Occhito in the southern part of Sheet 1) and, (6) the late Pliocene–lower Pleistocene claystones of the Bradanic Foredeep (in Sheet 2). Calabride Units The continuity of the Apenninic chain is truncated southward (few km south of Sheet 2, see Fig. 1) by the Sangineto line

Figure 7. Varicolored Scaly Clays (4av, “Argille variegate” or “Argille varicolori” of the Italian authors) of the Sicilide Units. Thinly bedded red, green and bluish clays alternating with calcilutites, cherty limestones and organic blackish horizons (Bonarelli level equivalent) in the overturned Calanche section, near Campomaggiore (see Sabato et al., 2007).

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that bounds the Calabria-Peloritani-Kabylie Terrane, first identified by Quitzow (1935) and termed “Complesso Calabride” by Ogniben (1969). South of the Sangineto line three rootless basement nappes of Hercynian metamorphic and intrusive rocks with different Mesozoic-Tertiary sedimentary covers crop out in Calabria (Sila, Serre, and Aspromonte) and in northeastern Sicily (Peloritani Mountains, Fig. 1). These units represent fragments of an eoAlpine chain, thrust over the Apenninic-Maghrebian belt of Sicily and North Africa during the early Miocene (Vai, 1992; Bonardi et al., 2001; Parotto and Praturlon, 2004). The provenance of this crystalline basement is controversial. The Calabride crystalline nappes have been interpreted either as (1) fragments of the European continental margin, accreted together with the ophiolite-bearing Liguride Units against the European margin during the Paleogene, and thrust above the outer Apenninic-Maghrebian chain in the early Miocene (Ogniben, 1969; Bouillin, 1984), or (2) units pertaining to the African continental margin, accreted with the ophiolitic nappes in the eo-Alpine Europe-verging orogenic belt (Haccard et al., 1972; Alvarez, 1976; Amodio Morelli et al., 1976). In the mapped area only limited outcrops are present in the southern part of Sheet 2, between Episcopia and Francavilla sul Sinni on the right bank of the Sinni River (see Plate 2) and described as “Undifferentiated Metamorphic Unit of Timpa Rotalupo” in the legend of the Geological Map (see Sheet 1). These outcrops consist of two major klippen of garnet gneiss, biotite gneiss, and marble (with overall thickness of 100– 200 m), with several lenticular blocks and thrust-bounded wedges of gneiss, amphibolite and marble. These units are accreted with the ophiolite-bearing rocks of the Episcopia mélange (see Spadea, 1982, for an accurate description), that tectonically overlies the Frido Formation (see next section). The overall setting remains obscure, and more research is needed for a better definition of the internal geometry and age of deformation. Liguride Units The Liguride Units include a heterogeneous group of ophiolite-bearing rocks, deformed by processes of subduction and collision, connected with the eo-Alpine (CretaceousPaleogene) episodes of Africa-Europe convergence. During the late Oligocene–early Miocene the Liguride Units were accreted onto the outermost units of the Apenninic thrust belt, where they occupy the highest geometric position (Ogniben, 1969; Ghisetti and Vezzani, 1982, 1983; Monaco et al., 1991; Monaco and Tortorici, 1994; Mazzoli, 1998; Elter et al., 2003). Two major tectonic units have been differentiated on the basis of age, structural setting and metamorphism: (1) the Frido Unit, and (2) the North Calabrian Unit. The “Frido Unit” is the lowest tectonic element of the Liguride Units. It consists of an Upper Jurassic to Lower Cretaceous succession with phyllites, quartzites, calcareous schists and marbles, interlayered with silty arenaceous limestones and deformed slices of ophiolites. This succession underwent high-pressure/

low-temperature subduction-related metamorphism, followed by greenschist-facies re-equilibration (Monaco et al., 1991; Monaco and Tortorici, 1995). Tectonically interleaved within the Frido Unit, there are blocks of a nonmetamorphic succession (Timpa delle Murge Formation of Bousquet, 1962; Vezzani, 1968a), consisting of a thin succession of pillow-lavas basalts, overlain by Late Jurassic–Early Cretaceous radiolarites, cherty limestones, shales and quartzarenites (Fig. 6). Other fragments of the Late Jurassic sedimentary succession that originally covered the pillow basalts are locally preserved in minor tectonic slices within the Frido Formation (e.g., Mezzana Limestones of Bousquet, 1962; Vezzani, 1968a). These sedimentary covers are too small to be represented in the 1:250,000 geological map. The Frido Unit is tectonically overlain by the “Episcopia Mélange” (Bonardi et al., 1988a), consisting of discontinuous, imbricated thin sheets of prevailing metapelites (granofels, garnet gneisses), associated with amphibolites, basic granulites and biotite gneisses, not differentiated in the 1:250,000 geological map. The presence of high-pressure/low-temperature rocks within this mélange could be interpreted as due to olistostromes and gravitative flows emplaced before the end of subduction, and subsequently deformed by tectonic processes (Spadea, 1982). Similar examples have been documented for other subduction settings (e.g., Franciscan Complex, see Hsü, 1968; Cowan, 1985; Shimabukuro et al., 2009; Wakabayashi, 2009). The “North Calabrian Unit” (Selli, 1962; Bonardi et al., 1988a, 1988b) is a thrust-bounded Cretaceous nonmetamorphic stack, comprising the Crete Nere and the Saraceno Formations (Fig. 10). The Crete Nere Formation (Vezzani, 1968c) consists of prevailing black shales alternated with thinly bedded siliceous calcilutites, marls and quartzarenites of Aptian-Albian age. This formation is stratigraphically overlain by the Saraceno Formation, a Late Cretaceous–Paleocene alternation of thin beds of turbiditic calcarenites, calcilutites with cherts in nodules, lithicarkosic sandstones and conglomerates (Vezzani 1968b). It is unconformably covered by the turbiditic succession of the Albidona top-thrust basin (3fa, Fig. 6). Outer Domains The tectonic units deriving from the progressive deformation of the outermost external Apenninic domains are characterized by carbonate platform/slope/basin systems and pelagic basins, originally located along the Adriatic-Apulia continental margin (Fig. 2). These successions (Fig. 4) were deposited during a sequence of processes, with (1) Permo-Triassic rifting and crustal extension; (2) establishment of deep seaways and pelagic basins during Triassic-Jurassic (Scandone, 1975; Marsella et al., 1995); and (3) block-faulting and dismembering of a wide platform domain that survived until the end of the Cretaceous, (Bernoulli, 2001). At present all these units (Lazio-Abruzzi and Campania-Lucania, Abruzzi and Umbria-Marche, LagonegroSannio, Sannio-Molise) are tectonically overlain by the Liguride and Sicilide Units.

Geology and Tectonic Evolution of the Central-Southern Apennines, Italy Lazio-Abruzzi and Campania-Lucania Units In the regions of Lazio, Abruzzi, Campania, and Basilicata, large exposures of carbonate massifs preserve features indicative of their original paleogeography (Fig. 2) with: (1) wide carbonate platforms separated by narrow seaways; (2) isolated peritidal carbonate platforms; and (3) flooded peritidal platforms, covered by condensed pelagic successions (Colacicchi, 1967; D’Argenio and Scandone, 1970; Amodio Morelli et al., 1976; Channell et al., 1979; Ghisetti and Vezzani, 1986a). The different facies that characterize these units (representing the platform interior, platform-edge, slope and pelagic basins) are well described in the literature (Colacicchi, 1967; D’Argenio et al., 1973; Parotto and Praturlon, 1975, 2004; Bernoulli, 2001; Ciarapica and Passeri, 2002; Bosellini, 2004; Passeri et al., 2008). In the study area, we differentiate two major tectonic units. The geometrically highest is the Verbicaro Unit (7dv, in outcrop only at the southwestern margin of Sheet 2), characterized by Triassic-Liassic dolomites and Jurassic cherty limestones, indicative of an original location at the internal margin of the LazioAbruzzi and Campania-Lucania carbonate platform. The cherty limestones are truncated by a Late Jurassic–Cretaceous unconformity, and overlain by Maastrichtian calcirudites and calcarenites with Orbitoides and Globotruncana. Locally, the cherty limestones were deposited during the Cretaceous, and are transgressively overlain by the Paleocene–lower Miocene calcarenites of the Trentinara Formation (Grandjacquet and Grandjacquet, 1962; Vallario and De Medici, 1967; Bousquet and Grandjacquet, 1969; Grandjacquet, 1971; Climaco et al., 1997). The Trentinara Formation is associated with dykes and flows of basic lavas (Quitzow, 1935). The geometrically lowest unit is the Pollino Unit (in outcrop at the south margin of Sheet 2), consisting of a monotonous succession of neritic carbonates, Triassic to Cretaceous in age (7pc). The platform carbonates are truncated by an unconformity; above it rest the Aquitanian-Burdigalian calcarenites (7bl) of the Cerchiara di Calabria Formation (Selli, 1957), gradually passing upward to the terrigenous succession of the Bifurto Formation (Selli, 1957; Vezzani, 1966; Vallario and De Medici, 1967; Dietrich and Scandone, 1972). The Pollino Unit correlates to the north with similar carbonate platform successions, in outcrop from northern Calabria (Mount Rossino) to Campania (Camposauro), Molise (Matese), Abruzzi (Marsica) and Lazio (Simbruini-Ernici Mountains). These units are all mapped as 7pc in the Geological Map (see Sheets 1 and 2). The Mesozoic platform carbonate successions are conformably overlain by Lithotamnium and Bryozoan calcarenites (Cusano and Cerchiara di Calabria Formations, 7bl), of early-middle Miocene age (Fig. 8), grading upward to the syntectonic siliciclastic successions of the Frosinone, Pietraroja, and Anversa degli Abruzzi Flysch (7a) that were deposited in a system of foredeep basins of late Tortonian to Messinian age (e.g., Cipollari and Cosentino, 1995; Cosentino et al., 2001).

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Abruzzi and Umbria-Marche Units These units include stratigraphic successions originally located in the transitional zone between the Lazio-Abruzzi carbonate platform and the Umbria-Marche basin (Fig. 2), each one possessing distinct stratigraphic evolution and facies (Colacicchi, 1967; Chiocchini et al., 1980; Ghisetti and Vezzani, 1988; Monaco, 1989; Bigozzi, 1994; Bertinelli et al., 2002, 2005a, 2005b; Passeri et al., 2008). Some of these units preserve a stratigraphic continuity from the Late Triassic to the late Miocene; others display an abrupt platform to basin transition starting with middle Lias synsedimentary rifting. In some units the progressive collapse of the platform edge is testified by repeated intercalations of thick bodies of calcareous turbidites and breccias associated with unstable fault scarps during the Jurassic (Parotto and Praturlon, 1975; Sgrosso, 1986; Bernoulli, 2001). The stratigraphic successions of these units (Fig. 8) include Upper Triassic–lower Liassic shallow-water carbonates overlain by platform scarp edge–proximal basin deposits (8sb), with variable amounts of platform-derived resediments. These deposits pass upward to ramp carbonates and hemipelagites (8bc), and are conformably covered by the lower Messinian siliciclastic turbidites of the Laga (8a) and Gran Sasso Flysch (Mutti et al., 1978; Koopman, 1983; Cantalamessa et al., 1986; Chiocchini et al., 1986; Milli et al., 2006). The major tectonic units deriving from this paleogeographic realm are the Gran Sasso–Mount Genzana Unit and the underlying Montagnone–Montagna dei Fiori Unit. Together, they are thrust over the Mount Porrara Flysch of the Outer Abruzzi Units (Mount Morrone) and the Teramo Flysch of the La Queglia– Colle Madonna Unit (see “Structural Scheme” in Sheet 2). Lagonegro-Sannio Units The paleogeographic reconstruction of Figure 2 shows the location of the wide basinal area interposed between the LazioAbruzzi, Campania-Lucania, and the Apulia carbonate platforms, where the successions of the Lagonegro, Sannio, and Molise Units were originally deposited (Mostardini and Merlini, 1986; Stampfli et al., 1991; Ciarapica and Passeri, 1998, 2002; Pescatore et al., 1999; Patacca and Scandone, 2007a). The deformation of this paleogeographic domain produced two major tectonic units: the Lagonegro-Sannio Units (described in this section) and the Sannio-Molise Units (described in the next section). The Lagonegro-Sannio Units occupy the lowest geometric position in the imbricate stack of the outer domains of southern Apennines (Fig. 4). They include a Middle Triassic (Mount Facito Formation) to Lower Cretaceous (Galestri Formation) basinal succession (Fig. 8), exposed at Mount Sirino and in several other tectonic windows of the southern Apennines (Fig. 9). No Upper Cretaceous to Miocene stratigraphic cover is present, and the causes of this gap have been widely debated in the literature (Selli, 1962; Scandone, 1963, 1967, 1972; Ogniben, 1969; Carbone and Lentini, 1990; Ciarapica et al., 1990; Marsella et al., 1993, 1995; Ciarapica and Passeri, 1998).

north

to the east

Figure 8. Outer domains: main stratigraphic successions and ages of the external units of the Apenninic chain. Time-space migration of shortening from the Tyrrhenian to the Adriatic zone is well reflected by the age (late Miocene to middle-late Pliocene) of the foredeep flysch deposits that are progressively younger from Unit 7 to Unit 14.

north

16 Vezzani et al.

Geology and Tectonic Evolution of the Central-Southern Apennines, Italy According to Ogniben (1969) the apical terms of the original Lagonegro succession were tectonically sliced and transported eastward in the “External Flysch” succession that crops out in the anticlinal ridge of Ripacandida-Stigliano-Colobraro (see Fig. 9). The tectonic elision of the topmost Lagonegro

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beds is also favored by Carbone and Lentini (1990), to explain: (1) the strong variations in thickness of the Galestri Formation; and (2) the affinity between the proximal facies of the Lagonegro succession and the Upper Cretaceous–early Miocene Mount Malomo Formation (Lentini and Vezzani, 1974) that overlies the

Figure 9. Tectonic windows of the Lagonegro Units and relationships with the structural highs of the Apulia-Adriatic deformed Units (Maiella, Casoli and Mount Alpi). See text for a discussion and interpretation.

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Lower Cretaceous Galestri Formation. Other Meso-Cenozoic successions with Lagonegro affinity, but with abundant calcareous clastic material (indicative of proximal facies) are distributed from Mount Moschiaturo (Molise region, Vezzani et al., 2004; Festa et al., 2006) to the area of San Fele–Bella in Basilicata. In our interpretation: (1) the Jurassic–Upper Triassic Cherty Limestones (9cs) of the distal Lagonegro-type succession were transitional to the cherty dolomites with calciruditic intercalations of the Pesche Formation (10g); and (2) the Scisti Silicei Formation (9ss) of the Lagonegro-Sannio Units were transitional to varicolored radiolarites alternating with calcareous breccias and calcarenites with nodular cherts. These units (Fig. 10) are in outcrop at San Fele (northern Basilicata), and correlate with the Mount Coppe Formation (10f) of the Sannio-Molise Units (described in the next section). Figure 11 shows the stratigraphic correlations and the position of the detachments between the Mesozoic and Cenozoic horizons of the Lagonegro-Sannio and Sannio-Molise Units. The interpretation that the proximal Sannio-Molise Units and the distal Lagonegro-Sannio Units were deposited in the same palaeogeographic domain (since the Late Triassic) was already advanced by Bertinelli et al. (2005b) and Passeri et al. (2005). Sannio-Molise Units The Sannio-Molise Units are exposed in a wide area from Molise to Basilicata (Fig. 9). The Mesozoic portion of the Sannio-Molise Units (“Coltri Sannitiche” of Selli, 1962) consists of cherty pelagic micritic limestones with repeated intercalations of thick beds of calcareous megabreccias (Late Triassic to Late Cretaceous). As described in the previous section (see also Bertinelli et al., 2005b; Passeri et al., 2005), the successions located at the base of the Sannio-Molise Units and attributed to the

Pesche (10g), Mount Coppe (10f), Coste Chiavarine, and Mount Calvello (10e) Formations (see Pescatore, 1965, 1988; Pescatore and Tramutoli, 1980; Pescatore et al., 1988, 1999) are interpreted as the lateral transition of the Cherty limestones (9cs), Scisti silicei (9ss) and Galestri Formation (9ga) of the distal LagonegroSannio Units (Figs. 8 and 11). The Cenozoic basinal to transitional succession of the Sannio-Molise Units (equivalent to the “Molise Units” of Vezzani and Ghisetti, 1998; Vezzani et al., 2004) is exposed along NW-SE ridges (Plate 1) from Pizzi (Abruzzi), to Frentani (Molise), to Daunia (Puglia) Mountains. Further south it is exposed along the Ripacandida-Stigliano-Colobraro ridge (Plate 2) till to the Ionian Sea, at the Basilicata-Calabria border (Fig. 9). At the base of this succession is the “Flysch Rosso” (10d1), deformed within a thick detachment zone at the boundary between the Mesozoic horizons, at the top of the Coste Chiavarine and Mount Calvello Formations (10e) and the overlying Cenozoic succession of the Sannio-Molise Units (Fig. 12). Above rests the Macchiagodena Formation (10d), stratigraphically followed upward by the Numidian Flysch (10q) and by the overlying marly-calcareous formations of Tufillo, Gamberale-Pizzoferrato (10b3), Faeto, and Serra Palazzo (10b4), all of Serravallian-Langhian age, passing upward to the Tortonian Orbulina Marls (10b1). The succession is closed by the turbidites of the Sant’Elena (10a2) and Agnone (10a3) Flysch of early Messinian–late Tortonian age, up to 2000 m thick (Selli, 1962; Crostella and Vezzani, 1964; Vezzani, 1975; Lanzafame and Tortorici, 1976; Clermonté, 1977; Clermonté and Pironon, 1979; Ciaranfi et al., 1980; Amore et al., 1988; Patacca et al., 1990, 1992a; Di Bucci and Scrocca, 1997; Corrado et al., 1998; Ghisetti and Vezzani, 1998; Di Luzio et al., 1999; Antonucci et al., 2000a, 2000b; De Corso et al., 2000; Pescatore et al., 2000; Matano and Di Nocera, 2001; Di Nocera et al., 2002; Festa et al., 2006).

Figure 10. Tectonic window of San Fele (Basilicata), with the “Scisti silicei” (Formation 9ss of the LagonegroSannio Units) emerging on the NE flank of a NW-SE faulted anticline. In red is the trace of the NW-SE normal fault shown in cross sections 5 and 6 in Sheet 2. The outcropping succession (Cretaceous-Jurassic) consists of thick beds of graded calcareous breccias and calcarenites with nodular cherts, alternating with red and green radiolarites and cherty argillites, in cm-thick beds. This Lagonegro-Sannio succession in proximal facies shows strong stratigraphic analogies with the Sannio-Molise Units (see Bertinelli et al., 2005a; 2005b; Passeri et al., 2005).

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Figure 11. Stratigraphic relationships between the Lagonegro-Sannio and the Sannio-Molise Units. Numbers are the same as in the legend of the Geological Map (in Sheet 1). The Sannio-Molise Units are interpreted as transitional proximal facies, detached from the original Lagonegro-Sannio basinal succession, that lack all the terms younger than the Early Cretaceous (Fig. 8). See text for a discussion.

Figure 12. Frontal view of the WNWstriking slope of Mount Morrone (Abruzzo), with subvertical to overturned beds of platform carbonates (11pt, Late Cretaceous–Malm), thrust above the Messinian Mount Porrara Flysch (11ag) along a low-angle SW-dipping thrust fault (marked in red). The Mount Porrara Flysch is on its turn thrust over the lower Pliocene Maiella Flysch (13f). The arrows mark the outcrops of the middle-lower Pliocene conglomerates of the Mount Coppe top-thrust basin (3cc) that unconformably cover the Mount Morrone carbonates (11pt). View from Caramanico.

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Outer Abruzzi Unit The Mount Morrone–Mount Porrara-Rocchette succession was originally located at the inner margin of the Apulia carbonate platform (Fig. 2). This unit is exposed along a narrow NNW-SSE ridge, tectonically interposed between the Gran Sasso–Mount Genzana Unit (hanging wall) and the Maiella Unit (footwall). The succession consists of prevailing facies of Paleodasycladus bearing limestones (middle-late Lias), followed by thick-bedded gray dolomites and dolomitic limestones (Dogger-Lias), alternating calcilutites, oolitic limestones and gray dolomites (Malm-Dogger), oolitic-bioclastic grainstones with corals, brown limestones with greenish clayey marls with Orbitolina spp., and thinly bedded (10–20 cm thick) mudstones and wackestones with bauxitic horizons (Late Cretaceous– Malm). These units in carbonate platform facies (see also D’Andrea et al., 1992) grade northward to platform edge and/ or scarp facies in the Late Cretaceous–Paleocene, as documented by calcirudites with Rudistid fragments interlayered with micrites containing planktonic foraminifera. Bryozoan and Lithotamnium calcarenites of early-middle Miocene age follow unconformably (Fig. 8) and pass upward to pelites with gypsum interlayers, bituminous marls and gypsum arenites grading to the Messinian Mount Porrara Flysch (Sartoni and Crescenti, 1964; Accordi, 1966; Pieri, 1966; Crescenti et al., 1969; Parotto and Praturlon, 1975; Accordi and Carbone, 1988). The northward transition of this platform domain to the pelagic Adriatic Basin is testified by the heteropy between the Mesozoic platform carbonates of the southern Morrone and the coeval successions with platform scarp edge-proximal basin facies of the northern Morrone (Vezzani and Ghisetti, 1998). The structural edifice of the Morrone Unit is composed of a number of NNW-SSE thrust sheets, arranged in a right lateral, en echelon system. The major structure is the E-verging

Mount Morrone anticline that overthrusts the Maiella Unit along the western border of the Caramanico trough (Figs. 12 and 13). To the south, the imbricate thrust sheet of Mount Porrara overrides the southern part of Maiella at Guado di Coccia. At Mount Arazzecca (south of Roccaraso) the Outer Abruzzi Units deflect from NW-SE to NNE-SSW orientation and design a broad arcuate front, overridden by the Sannio-Molise Units to the west. Farther south, the Outer Abruzzi Units disappear underneath the carbonate platform-to-basin succession of Meta Mountains (8sb), the platform carbonates of Matese Mountains (7pc), and the Molise-Sannio Units of Montenero Valcocchiara (see Plate 1), as documented in the tectonic window of PizzoneRocchetta a Volturno. La Queglia–Colle Madonna–Teramo Unit This unit consists of ramp carbonates (12d) in “Maiolica” and “Scaglia” facies, with intercalations of calcareous rudites (Cretaceous-Eocene), uplifted in the core of the tight anticline of La Queglia, and unconformably overlain by the glauconitic calcarenites of the Bolognano Formation (middle-early Miocene), that grade upward to the Serravallian-Messinian Orbulina Marls (12c). These are followed by Messinian terrigenous and evaporitic deposits (12b in Fig. 8). On top are the Teramo Flysch and Vomano Marls (postevaporitic–Messinian–early Pliocene, 12a), containing a horizon of acid volcano-clastics rocks (5.5 Ma according to Patacca and Scandone, 2007a; see also Bigi and Di Bucci, 1987; Ori et al., 1991; Ghisetti et al., 1994). This succession is exposed along a narrow N-S belt (2– 3 km to 10 km wide), from the Salinello River (to the north) to the Pescara River (to the south, see Plate 1), where the unit is truncated by the overlying Gran Sasso–Mount Genzana overthrust (Ghisetti et al., 1994). The La Queglia–Colle Madonna–Teramo Unit is deformed in up-thrusted folds with vertical to overturned

Figure 13. Cross-section view on the structure of Mount Morrone along the right bank of the Vella River (view from San Germano, along the road Campo di Giove–Guado San Leonardo). The oucropping succession of the Mount Morrone Unit consists of: (A) basal member of thick-bedded gray dolomitic limestones (Dogger-Lias); (B) alternating calcilutites and oolitic limestones (Malm-Dogger); (C) bioclastic grainstones with corals, greenish marls with Orbitolina spp., mudstones and wackestones with bauxitic horizons (Late Cretaceous–Malm). The inset shows in detail the structure of the Mount Morrone thrust front, with the overturned fold (bedding marked in white) of the Upper Cretaceous platform carbonates thrust over the Mount Porrara Flysch (11ag, not visible in the photograph).

Geology and Tectonic Evolution of the Central-Southern Apennines, Italy limbs, interposed between the Abruzzi and Umbria-Marche Units in the hanging wall and the Maiella Unit in the footwall (Vezzani and Ghisetti, 1998). Maiella and Mount Alpi Units The successions exposed in the Maiella Unit and in the underlying Casoli Unit (Abruzzi region) as well as at Mount Alpi (Basilicata region) are the geometrically deepest tectonic elements of the Apenninic chain. They emerge at the surface in a series of tectonic windows and represent the major structural culminations of the Apulia-Adriatic deformed Units (Fig. 9). The Maiella Unit consists of a succession of platform carbonates of late Malm–Oligocene age. The oldest terms crop out on the eastern flank of the Maiella with an alternation of ooliticoncolitic calcarenites and thin stromatolitic layers (Malm–Early Cretaceous), that grade upward to detritic limestones with Rudistid fragments and bauxitic lenses (Mount Acquaviva Formation of late Campanian–Maastrichtian age). The shallow-water Upper Jurassic–Lower Cretaceous carbonate platform (with bauxites) shows a spectacular facies transition to the north (see geological map in Vezzani et al., 1993) toward a succession of platform edge-proximal basin that onlaps the platform carbonate along a basal surface dipping 35° N (see Mutti et al., 1996; Lampert et al., 1997; Vecsei et al., 1998; Bernoulli, 2001). The overlying basinal succession of CenomanianOligocene age hosts repeated lenses of north-channelled breccias and resedimented limestones, fed by the unstable platform margin. The Maiella Unit is closed upward by the transgressive Bryozoan and Lithotamnium calcarenites of the Bolognano Formation (early Miocene–Tortonian), stratigraphically followed by tripolaceous and gypsiferous mudstones of the Messinian “Gessoso-Solfifera Formation” and upper Messinian “lago-

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mare” deposits (Crescenti et al., 1969; Eberli et al., 1993; Bernoulli et al., 1996; Mutti et al., 1996; Vecsei et al., 1998; Cipollari et al., 2003; Cosentino et al., 2005; Sampalmieri et al., 2008). On top rests the lower Pliocene Maiella Flysch (up to 1000 m thick) with, at its base, a thin (40–50 m) horizon of breccias and calcareous conglomerates (Roccacaramanico and Palena Conglomerates, see Casnedi and Mosna, 1992) of early Pliocene age (lower part). To the north of the Pescara River, the Maiella Flysch passes to the overlying marly claystones with megaturbiditic sands of the Cellino Formation (Casnedi et al., 1976; Casnedi, 1983, 1991), grading to the bluish marly clays of the Montefino Formation, containing Globorotalia puncticulata (upper part of the early Pliocene, see Vezzani and Ghisetti, 1998), as shown in the NNW-SSE longitudinal cross section traced from Mount Amaro to the Montefino 1 well (Fig. 14). The Maiella Unit is truncated to the west by the leading thrust faults of the overlying La Queglia–Colle Madonna– Teramo and Outer Abruzzi Units (Mount Morrone, Fig. 12). To the SE the eastern flank of the Maiella anticline is overridden by the Sannio-Molise Units, along a belt of W-verging imbricate wedges involving also the Sicilide Units. Thus, the whole structure of the Maiella Unit is a complex tectonic window, truncated to the west by the Caramanico normal fault (Fig. 15) and open to the north, where the anticline plunges underneath the clastic deposits of late-middle Pliocene age of the Castilenti top-thrust basin (Ghisetti and Vezzani, 2002a). In Basilicata, Mount Alpi emerges as a normal fault-bounded structural high, piercing through the overlying allochthonous Lagonegro-Sannio and Liguride Units. The stratigraphic succession of Mount Alpi comprises 800–1000 m of Upper Jurassic– Lower Cretaceous limestones of carbonate platform facies (Sgrosso, 1988) truncated by an unconformity, and overlain by

Figure 14. Longitudinal cross section along the N-plunging axis of the Maiella anticline and parallel to the W-dipping Caramanico normal fault (see also Figs. 15 and 29). Data from exploration wells in the Cellino gas field demonstrate the northward continuity of the Maiella structure in the subsurface. The steep northward plunge of the Maiella anticline SSE of the Cigno 2 well is caused by the late differential uplift of the Maiella anticline, imposed by accumulation of large displacements on the Caramanico fault after 1.6 Ma. Note the decrease in displacements from SSE to NNW (modified after Ghisetti and Vezzani, 2002a).

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Vezzani et al. Figure 15. Aerial view eastward of the increasing uplift in the central Apennines carbonate platform. The platform carbonate successions of Montagna Grande (7—Lazio-Abruzzi Units) and Mount Genzana (8—Abruzzi and Umbria-Marche Units) are overthrust to the east onto the successions of Mount Morrone–Mount Porrara (11—Outer Abruzzi Units). In the background to the east is the deformed and strongly uplifted foreland of the Apenninic chain represented by Maiella (13—ApuliaAdriatic deformed Units), culminating at Mount Amaro (2795 m asl), the second highest peak of the Apennines. The Maiella emerges as a N-S–striking, doubly plunging anticline, truncated on its western flank by the Caramanico normal fault (see Fig. 14). The eastern flank of the anticline designs a large half dome (see Fig. 34) and is overthrust by the Sannio-Molise and by the Sicilide Units in the hazy Adriatic coastal region.

Messinian biocalcarenites, calcilutites and mudstones (Fig. 16). Above lie discordant polygenic and heterometric conglomerates dated to the early Pliocene by Patacca and Scandone (2007b). These upper horizons are relatable to the top-thrust clastic deposits of the Mount Coppe succession (see Ghisetti and Vezzani, 1986a). The geometric position of the Mount Alpi Unit suggests a correlation with the buried Apulia-Adriatic deformed Units. However, we do not have decisive stratigraphic constraints for a correlation with the Mount Morrone (Outer Abruzzi Units) as tentatively proposed by Patacca and Scandone (2007a), or alternatively to the Maiella Unit, as favored in our Geological Map (Sheets 1 and 2). Casoli Unit The Casoli Unit emerges in a tectonic window east of the Maiella, beneath the Sicilide and Molise-Sannio Units (Fig. 17). Only the uppermost lower Pliocene Torrente Lajo Flysch is in outcrop, followed downward (in the subsurface) by few meters of pelites with Sphaeroidinellopsis spp. (basal early Pliocene), Gessoso-Solfifera Formation (Messinian) and Bryozoan and Lithotamnium calcarenites of the Tortonian–lower Miocene Bolognano Formation (Mostardini and Merlini, 1986; Sella et al., 1988; Vezzani and Ghisetti, 1995, 1998; Vezzani et al., 2004; Festa et al., 2006). The buried succession crossed by the Fara 1 well (see also Crescenti, 1975; Patacca et al., 1992b; D’Andrea et al., 1993; Ghisetti et al., 1994) defines a NW-SE, E-verging anticline with wavelength of ~4 km and an axial trace exposed for a length of ~10 km (see cross section 2 in Sheet 2). The anticline is truncated by a bedding-parallel thrust fault with the Varicolored Scaly Clays of the Sicilide Units in the hanging wall (Fig. 17; see also cross section 2 in Sheet 2).

Apulia Foreland The Plio-Pleistocene Adriatic-Bradanic Foredeep (Fig. 3) is continuous from the Po Plain to the Adriatic coast of Marche, Abruzzi and Molise, to the Bradanic trough (between the Apennines and the Gargano-Murge), and to the Ionian coast of the Basilicata-Calabria regions. The trough is well traced by the contours to the top of the buried Mesozoic-Cenozoic carbonates of the Apulia Foreland (see BSCSA in Sheet 1). The peripheral bulge of this foredeep-foreland system is developed from the northern Adriatic to the Gargano and Murge peninsula (Fig. 3) and constitutes the major upper crustal structural element related to the subduction of the Apulia continental lithosphere beneath the accretionary prism of the Apennines. The Adriatic-Bradanic Foredeep is filled with the upper Pliocene–lower Pleistocene bluish claystones of the Mutignano Formation (2a), passing upward to the Sands of Serracapriola (2s) and to the Campomarino Conglomerates (2sc) described in the legend (Sheet 1). This succession is indicated with the key IP-eP in the cross sections 2, 3, 4, and 10 (see legend of “Undifferentiated Buried Successions” in Sheet 2), where it overlies stratigraphically the buried Apulia Foreland. The Apulia Foreland succession consists of Meso-Cenozoic platform carbonates that stratigraphically overlie Triassic evaporites and late Paleozoic siliciclastic units. This cover succession overlies a late Paleozoic, low-grade metamorphic basement, drilled at depths >7 km by the Puglia 1 well (Vai, 2001). The outcropping succession of the Apulia carbonate platform (up to 6 km thick) shows a lateral transition to platform edgebasin facies both to the east (East Gargano and Ionian Basin) and to the north (North Gargano and Tremiti Islands), where it passes to a domain characterized by ~4 km of Mesozoic-Cenozoic

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Figure 16. Strongly uplifted foreland of the Apenninic chain in Basilicata. Frontal view of the Mesozoic carbonate platform of the Apulia-Adriatic deformed Units (13pt) emerging in the structural high of Mount Alpi (see “Structural Scheme” in Sheet 2 and Fig. 9). The Lower Cretaceous–Upper Jurassic limestones of Mount Alpi (13pt), overlain at Mount Teduro by Messinian biocalcarenites, calcilutites and mudstones (13ma, see cross section 9 in Sheet 2), are strongly uplifted by a major N-S– striking normal fault (see “Buried Structure of the Central-Southern Apennines” in Sheet 1 and text for a discussion). In the pastures in the foreground outcrops the argillitic succession of the Lower Cretaceous Crete Nere Formation (6cn, Liguride Units) that tectonically overlies the Galestri Formation of the Lagonegro-Sannio Units (cross section 9 in Sheet 2). At the northern end of the photograph are the Jurassic–Upper Triassic Cherty Limestones (9cs) of Mount Armizzone (Lagonegro-Sannio Units). Photograph by Rocco di Perna.

pelagic limestones, connected with the Adriatic, Marche and Umbria basin (Fig. 2). A number of commercial seismic reflection lines and drillings provide a tie between the emergent foreland of the Gargano-Murge region and the substratum buried underneath the thick siliciclastic infilling of the Bradanic Foredeep and underneath the Apenninic thrust belt (Carissimo et al., 1963; Mostardini and Merlini, 1986; Sella et al., 1988; Ghisetti et al., 1993a; Casero, 2004; Nicolai and Gambini, 2007). This setting is summarized by the structural contour map of the top of the carbonate platform (BSCSA in Sheet 1; modified after Nicolai and Gambini, 2007). This map shows the lateral extent of the Apulia foreland (yellow to dark-brown colors in BSCSA, Sheet 1) flexed beneath the allochthonous Apenninic thrust belt and its progressive westward shortening in the buried Apulia-Adriatic deformed Units (blue to dark-blue colors in BSCSA, Sheet 1) that emerge in the tectonic windows of Mount Alpi, Maiella,

and Casoli (Fig. 9). The deep structure of the buried top of the Apulia Foreland (color key 15) and of the buried Apulia-Adriatic deformed Units (color key 13–14) is reconstructed in all the cross sections of Sheet 2. REGIONAL STRUCTURAL SETTING The present structural configuration of the Apennines results from noncoaxial deformations, with superposed regimes of contraction (Paleogene-Miocene to Pliocene) and extension (late Miocene to early Pleistocene), migrating in time from west to east, toward the outer domains (Fig. 3; see also Ghisetti and Vezzani, 1999; Grasso, 2001; Elter et al., 2003; Parotto and Praturlon, 2004; Ghisetti and Vezzani, 2002a). The present finite deformation (Fig. 4) depends strongly on the regional location within the thrust belt (i.e., inner versus outer

Figure 17. Western flank of the Casoli tectonic window, showing the overthrust of the Varicolored Scaly Clays (4av, Sicilide Units) above the lower Pliocene gray-whitish marly clays of the Torrente Lajo Flysch (14a). The Varicolored Scaly Clays are characterized by a block-in-matrix structure, with blocks of varying dimensions (dm-m) and lithology (Miocene limestones and marls of the Molise Units, lower Pliocene bluish clays of the Maiella Flysch). The whitish marly clays (early Pliocene) of the footwall are truncated by a beddingparallel thrust fault (in red) that dips 20° WSW (see the anticlinal setting of the Casoli window, to the east of Palombaro, in cross section 2 in Sheet 2). Modified from Festa et al. (2006).

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domains) and on the chronology of superposed extension versus shortening (Malinverno and Ryan, 1986; Royden et al., 1987; Patacca et al., 1992b; Ghisetti and Vezzani, 1997, 1999; Cavinato and De Celles, 1999). However, strong additional controls are exerted by the lithological competence contrasts between the imbricated units. Some units (e.g., Umbria-Marche, Sicilide, Liguride, Lagonegro-Sannio, Sannio-Molise) are characterized by repeated layer-parallel detachments within low-competence multilayers dominated by pelitic horizons. In other units (e.g., Lazio-Abruzzi and Campania-Lucania, Outer Abruzzi) localized deformation and buttressing occur in zones of competence contrast between the Mesozoic carbonate platforms and the coeval pelagic successions (Ghisetti and Vezzani, 1997). Finally, rigid deformations and block faulting characterize the thick (up to 7– 8 km) and lithologically monotonous carbonate successions of the Lazio-Abruzzi and Campania-Lucania Units and of the Apulia-Adriatic deformed Units (Maiella and Mount Alpi; see Ghisetti and Vezzani, 1997, 1999). Overall, the inherited paleogeography of the Apulian margin (e.g., Bally et al., 1986; Dercourt et al., 1986; Cavazza and Wezel, 2003; Elter et al., 2003; Patacca and Scandone, 2007a) facing the Tethyan Basin dictates the position of re-entrants and salients of the rigid units (Fig. 2) and it is one of the primary causes for the observed disharmonic deformation, with: (1) sharp deflections of tectonic trends, and (2) strong variations in intensity of shortening/elongation, geometrically accommodated by detachments, rotations, and transfer faulting. Significant along-strike variations in the geometry and morphology of the whole Apenninic chain are controlled by the facies transitions (Fig. 2) between the Apulia and Lazio-Abruzzi platforms (to the south) and the Umbria-Marche basins (to the north). These transitions are clearly visible in outcrop (e.g., at Mount Morrone and Maiella) and well documented in the subsurface, and are also reflected by the differential flexural elasticity of the Apulia lithosphere, resulting in along-strike variations in depth, width, and sedimentary accommodation space of the Adriatic-Bradanic Foredeep (Royden and Karner, 1984; Royden et al., 1987; Faccenna et al., 2004; Rosenbaum and Lister, 2004). Geometry of the Thrust Belt The thrust belt of the central-southern Apennines provides good examples of strong lateral variations in shortening and/or elongation, associated with syntectonic rotations and propagation of out-of-sequence thrust faults (e.g., Ghisetti and Vezzani, 1983, 1986a, 1990, 1991, 1997; Royden et al., 1987; Ghisetti et al., 1990; Dela Pierre et al., 1992; Grasso, 2001). The finite structure of the thrust belt (Fig. 4) results from progressive shortening, thrust propagation, outward tectonic transport of the allochthonous thrust sheets and deformation of the imbricate stack by involvement of progressively deeper units (Fig. 18). This setting is illustrated in “Structural Scheme” (in Sheet 2) and in the cross sections (Sheet 2), and will be briefly outlined in the following.

In general, shortening and structural complexity in the Apenninic chain decrease from the internal (western) to the external (eastern) domains, together with the regional eastward younging of contractional deformation (Fig. 4). Inner Units The western segment of the South Apenninic thrust belt in the Campania and Basilicata regions preserves portions of the most internal structural domains. These domains are characterized by Paleogene contractional structures involving the far traveled eo-meso-Alpine units of Tethyan affinity (Liguride Units) and the European foreland (Calabride Units) that were subsequently thrust over the outer domains (e.g., the CampaniaLucania platform). Starting with the early Miocene, younger episodes of shortening affected the units of the underlying Campania-Lucania platform, resulting in the overall deformation of the already emplaced Liguride-Calabride imbricates. The whole imbricate stack was subsequently crosscut by a later set of NW-SE Pliocene–early Pleistocene normal faults, active during the extension, foundering and crustal thinning of the Tyrrhenian Basin (Figs. 1 and 3) and the strong uplift of the Apenninic thrust belt (Cinque et al., 1993; Westaway, 1993). The axial zone of this westernmost internal domain is characterized by a N-S anticline/syncline system, culminating in the tectonic windows of the Lagonegro Units at Mount Sirino (see Fig. 9). The culmination and surface exposure of the ApuliaAdriatic deformed Units at Mount Alpi is connected with the Pliocene activity of high-angle normal faults (cross section 9 in Sheet 2; see Fig. 16), alternatively interpreted by Van Dijk et al. (2000) as transpressive back-thrusts. To the west (Mount Sirino) and to the north (Armizzone) of Mount Alpi, the Lagonegro Units are deformed by sets of prePliocene, N-S oriented, tight isoclinal folds, refolded by later N-S open anticlines of Pliocene-Pleistocene age (Cinque et al., 1993). Outer Units In these domains, the outcrops of the Sicilide and SannioMolise Units prevail. The succession of the Sannio-Molise Units is interpreted as detached from the Lagonegro substratum (see Pescatore et al., 1999; Menardi Noguera and Rea, 2000; Di Nocera et al., 2006) along a series of shear planes within the early Miocene–Late Cretaceous Flysch Rosso (Fig. 11), and transported to the E-NE, where it outcrops along the FrentaniDaunia-Ripacandida-Stigliano-Colobraro ridge (Fig. 9). Within this ridge, E-verging folds and thrust faults deform the SannioMolise Units (Fig. 18), the tectonically interleaved slivers of the Sicilide Varicolored Scaly Clays, and the top-thrust deposits of the Mts. Frentani Clastic-Evaporitic Succession (3dg). This is the so-called Frentani Tectonic Mélange (Vezzani et al., 2004; Festa et al., 2006, 2010a, 2010b). All together, these units were transported above the late Pliocene–early Pleistocene siliciclastic succession of the Adriatic-Bradanic Foredeep (Fig. 9, and cross sections 3, 4, 5, 6, and 7 in Sheet 2) that, in turn, onlaps the

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Figure 18. Regional distribution of the major contractional structures (thrust faults and folds) in the mapped area. The regional thrust faults separate stratigraphic-structural units characterized by distinct lithological successions (numbers are the same as in the legend of the Geological Map, Sheet 1). See text for a discussion.

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Cretaceous limestones of the Apulian Foreland and the overlying upper Miocene Apricena Calcarenites (cross sections 4, 7, and 10 in Sheet 2). From Abruzzi to northern Calabria, the FrentaniDaunia-Ripacandida-Stigliano-Colobraro ridge is bounded to the east by some of the outermost culminations of the Apulia carbonate platform (Montorio dei Frentani in Molise, Pisticci, Rocca Imperiale and Montegiordano in Basilicata; southeastern part of Sheet 2; see Figures 9, 18, and BSCSA in Sheet 1). Foreland The outermost domain is the Adriatic-Apulia Foreland, in outcrop in the Gargano Promontory and along the MurgeSalento Peninsula (Figs. 1 and 3). The structure of this domain is simple and already well documented in previous regional maps (Ciaranfi et al., 1988). The platform carbonates succession is weakly deformed in a large, open anticlinal dome with NW-SE axial trend, continuous from the Salento to the Gargano Promontory, the Tremiti Islands, and the Adriatic Sea (Fig. 3). This structure corresponds with the peripheral bulge of the flexed foreland (Royden and Karner, 1984; Royden et al., 1987) that continues northwards in the Adriatic Sea (Ghisetti and Vezzani, 1999; Nicolai and Gambini, 2007) and is well traced by the contours to the top of the carbonates (see BSCSA in Sheet 1). First-Order Structures of the Thrust Belt The major structures of the Apenninic thrust belt will be described proceeding from north (Sheet 1) to south (Sheet 2). In the Abruzzi region (Sheet 1) the geometry of the Apenninic thrust belt (Fig. 18) is dominated by the large-scale interfer-

ence of discordant structural trends, resulting from the interplay between: (1) inherited paleogeography of the Mesozoic carbonate platforms (Fig. 2); (2) differential shortening between rigid carbonate platform successions and the low competence multilayer of the basinal successions; (3) syntectonic rotations above multiple detachments horizons; and (4) irregular trajectories of thrust fault propagation across successions with strong competence contrasts, resulting in fault segmentation against rigid indenters, and out-of-sequence propagations within the imbricate stack (Ghisetti and Vezzani, 1991). The development of noncoaxial tectonic trends has one of the best examples along the arcuate (E-W to N-S striking) Gran Sasso thrust front (Figs. 19, 20, and 21), where the Messinian Gran Sasso Flysch (8aa) overrides the Messinian Laga Flysch (8a) of Montagnone (Abruzzi and Umbria-Marche Units). The frontal imbrication is characterized by tight, E-W–striking overturned folds, decapitated by the late propagation of out-ofsequence thrust faults (Figs. 22 and 23). To the east of Mount Prena and of Mount Camicia, the Gran Sasso thrust front gradually rotates to ENE-WSW and N-S orientations, with tectonic superposition above the Teramo Flysch (12a) of the La Queglia– Colle Madonna–Teramo Unit (Fig. 24). The E-W–striking segment of the Gran Sasso thrust front truncates in its footwall a N-S–striking system of progressively outer and younger folds and thrust faults (see “Structural Scheme” in Sheet 2), whereas the N-S–striking segment rests tectonically above the subparallel footwall structures of Colle Madonna (Figs. 25 and 26) and La Queglia (Figs. 27 and 28; Ghisetti et al., 1993b). Shortening increases northward toward the Gran Sasso thrust front. Its E-W trend is consistent with the upper Messinian–lower Pliocene

Figure 19. Sunrise at Corno Grande (Gran Sasso thrust belt, Abruzzi), the highest peak of the Apenninic chain (2912 m asl). Lower Jurassic massive platform limestones (“Calcare Massiccio,” 8sb), tectonically sliced in several imbricates, are overthrust onto the overturned flank of a syncline that deforms a basinal succession of MesozoicCenozoic age. In the immediate footwall of the major thrust fault (T1) is the S-dipping overturned succession from Lower Cretaceous–Jurassic Maiolica Formation to the Messinian Gran Sasso Flysch (8aa), that is on its turn overthrust (thrust fault T2) onto the upright section of the Montagnone, partly covered by the clouds in this photograph, but well exposed on the steep frontal scarp (see Fig. 20). In the footwall of thrust fault T2 crops the Messinian Laga Flysch (8a) and the underlying succession from the Messinian–upper Tortonian Orbulina Marls to the middle-lower Miocene Marne con Cerrogna-Bisciaro (8bc). Photograph by Anna Bigozzi.

Geology and Tectonic Evolution of the Central-Southern Apennines, Italy

Figure 20. Panorama on the northern frontal scarp of the Gran Sasso thrust belt. The “Calcare Massiccio” of the Lower Jurassic carbonate platform is in outcrop at Corno Grande and dips to the NNW beneath the pelagic cherty limestones of the “Corniola” and the mudstones of the “Verde Ammonitico,” deposited in a proximal pelagic basin adjacent to the platform (refer to Figure 2 for the paleogeography). These thinly bedded formations, in outcrop in the saddle west of Corno Grande (Sella dei due Corni), are stratigraphically overlain by the massive beds of the “Entrochi Calcarenites” of Corno Piccolo that are overthrust (thrust fault T1 dipping 20–40° S) onto the overturned flank of an E-W–striking asymmetric fold, deforming the basinal succession of Messinian–Late Jurassic age. This overturned succession (in outcrop north of Corno Piccolo) includes the formations of “Maiolica,” Rudistid Calcirudites, “Scaglia,” “Marne con Cerrogna,” and Orbulina Marls (see Ghisetti and Vezzani, 1990, and Ghisetti et al., 1990, for details). The subparallel thrust fault T2 truncates the succession between the Gran Sasso Flysch (8aa) in the hanging wall and the Laga Flysch (8a) in the footwall. T2 thrusts the whole E-W–striking Gran Sasso edifice onto the N-S–striking Montagnone anticline (right-hand side of the photograph). Note that the basal thrust fault T3 that duplicates the Montagnone succession is N-S striking. In the footwall of the Gran Sasso overthrust (to the east of La Madonnina), the Messinian Laga Flysch (8a) is covered by remnants of Quaternary breccias and conglomerates (Q-br).

Figure 21. Panorama of Pizzo d’Intermesoli and Mount Corvo, in the western segment of the Gran Sasso thrust belt. View from Prati di Tivo. The succession of the Abruzzi and Umbria-Marche Units (8sb) is folded along an E-W–striking anticline with a gently N-dipping upright limb, and a steep, S-dipping overturned limb. The fold is truncated by an E-W–striking, S-dipping subhorizontal frontal thrust fault (T1) propagating across the anticlinal hinge. One more thrust fault (T2) superposes the overturned fold limb over the Gran Sasso Flysch (8aa). The whole E-W–trending edifice of the Gran Sasso chain is translated by the lowermost, subparallel thrust fault T3 and thrust over the Messinian Laga Flysch (8a), which stratigraphically overlies the “Marne con Cerrogna” (8bc) of the Montagnone succession (see Figs. 19 and 20). The outcrop above the village of Pietracamela is made of cemented Quaternary breccias (Q-Br).

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Figure 22. Panorama of the northern slope of Mount Prena in the Gran Sasso thrust belt (Lazio-Abruzzi Units). The Mount Prena Triassic dolomites (7pc) are thrust over a Mesozoic-Cenozoic platform scarp edge-proximal basin succession (8sb) folded into a tight syncline, with a flattened, S-dipping overturned limb. The E-W–striking and S-dipping thrust fault (in red) truncates the synclinal hinge (in Corniola Formation, Jurassic) and propagates upward across the overturned limb, decapitating the wellbedded, low competence succession of the “Maiolica” (Early Cretaceous– Malm) and “Scaglia” (Eocene–Late Cretaceous) Formations (see Ghisetti and Vezzani, 1986a, 1986b, for details).

Figure 23. Panorama of the steep north slope of Mount Camicia, in the Gran Sasso thrust belt (Abruzzi). The village of Castelli is in the foreground. The erosional surface exposes: (a) the thrust front of Mount Prena (T1) between Mount Prena and Pietra della Spia, that superposes the Lazio-Abruzzi Units (7pc) to the Abruzzi and Umbria-Marche Units (8sb), and, (b) the frontal overthrust of Mount Camicia (T2), with steeply NNE-dipping beds of the “Corniola” Formation (Jurassic) in the hanging wall (along the crest from Mount Camicia to Dente del Lupo), and the folded Mesozoic-Cenozoic succession of carbonate proximal basin (continuous from the “Corniola” to the “Marne con Cerrogna” Formations) in the footwall. This is one of the best examples of out-of-sequence thrusting in the Gran Sasso thrust belt (see Ghisetti and Vezzani, 1986a, 1986b, 1991), with decapitation of an overturned, flattened syncline in the footwall (trace of bedding indicated on the photograph), with an E-W–striking subhorizontal axial surface (gently dipping to the south), that is tectonically superposed (T3) above a narrow E-W strip of alternating sandstones and clays of the Messinian Gran Sasso Flysch (8aa). In the footwall of the NNW-SSE thrust fault T4 are the claystones of Castelli belonging to the lower Pliocene–postevaporitic Messinian Teramo Flysch (12a). Photograph by Pino dell’Aquila.

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Figure 24. Panorama (view from Cima Alta, Montagnone) of the eastern segment of the E-W–striking Gran Sasso frontal overthrust (Abruzzi and UmbriaMarche Units, 8). The frontal scarp reaches up to 2000 m of relief. The thrust front of Mount Prena (T1) is the highest in the tectonic pile and superposes the platform carbonates of the Lazio-Abruzzi Units (7pc) to the scarp edge-proximal basin succession of the Abruzzi and Umbria-Marche Units (8sb). The latter are folded into a tight syncline, with a flattened, S-dipping overturned limb. East of Mount Camicia (at the left of the image) the frontal thrust gradually rotates from E-W to N-S strike, describing the large-scale Gran Sasso–Mount San Vito–Mount Picca arcuate thrust front (Ghisetti and Vezzani, 1997). The N-S– striking arm of this thrust front is partially depicted in Figures 25, 26, and 27; see also “Structural Scheme” in Sheet 2. The village of Castelli is in the background. Quaternary breccias are indicated by Q-Br. In the foothills are the footwall units deformed by N-S folds and thrust faults, decapitated by the overlying E-W frontal thrust fault T2. From west to east, the Gran Sasso overthrust overlies formations of progressively younger age belonging to different units: the Messinian Gran Sasso Flysch (8aa) tectonically overlying (thrust T3) the lower Pliocene–postevaporitic Messinian Teramo Flysch (12a). In the background, label 13a indicates the lower Pliocene Montefino and Cellino Formations. This setting is indicative of the post lower Pliocene out-of-sequence transport of the imbricated Gran Sasso Units, eventually associated with anticlockwise rotations along sets of shallow-dipping detachments (see Dela Pierre et al., 1992).

anticlockwise rotations inferred from paleomagnetic data (Dela Pierre et al., 1992). The Gran Sasso thrust belt provides one of the best studied and representative examples of arcuate thrust fronts in the Apennines (Fig. 18; see also Ghisetti and Vezzani, 1986a, 1986b, 1988, 1991, 1997; Ghisetti et al., 1990, and references therein), but other arcuate fronts are developed. An arcuate thrust front, deflected from E-W to NW-SE to N-S trends, characterizes the leading thrust front of the Abruzzi and Umbria-Marche Units at the northern thrust front of the Meta Mountains (S of latitude 41°48′ in Sheet 1; see also Figure 18 and “Structural Scheme” in Sheet 2). The N-S arm of the Gran Sasso thrust front, continuous southward with the Mount Genzana and Meta thrust belt, overrides the La Queglia–Colle Madonna–Teramo Unit, to the north (Figs. 26, 27, and 28) and the Mount Morrone, Mount Porrara and “Rocchette” Units, to the south (see Plate 1). In the area of Pizzone– Castel San Vincenzo, located to the south of the divide between the Sangro and the Volturno rivers, calcareous successions ascribed to the Outer Abruzzi Units are shortened and rotated up to vertical in a series of W-verging, NW-SE to N-S striking thrust wedges interposed between the Meta Mountains thrust in the hanging wall and the Sannio-Molise Units in the footwall. The Maiella (Fig. 15) together with the adjacent, minor structure of Casoli (Fig. 17) is the largest outcropping anticline of the Apulia-Adriatic deformed Units in the central Apennines (Fig. 29). It emerges as a tectonic window that pierces the Sicilide, Sannio-Molise Units and the overlying upper Pliocene– lower Pleistocene sediments of the Adriatic-Apulia Foredeep (Vezzani et al., 1993; Vezzani and Ghisetti, 1998).

The Maiella is a broad N-S–trending anticline with northward axial immersion of the Meso-Cenozoic calcareous succession beneath the lower Pliocene Maiella Flysch and the Montefino and Cellino Formations (Figs. 14). To the south the axis of the Maiella anticline plunges southward and disappears at Guado di Coccia beneath the leading thrust fault of the Mount Morrone Unit (Sheet 1). The surface exposure of the Maiella Unit results from the interplay between the anticlinal culmination and the late crosscutting of its western and eastern flanks by sets of upper Pliocene NNW-SSE normal faults (see Ghisetti and Vezzani, 2002a). The most prominent fault is the Caramanico fault, on the western flank of the Maiella anticline (Figs. 15 and 29). In Figure 9 (see also Fig. 18 and BSCSA in Sheet 1), the surface geometry is tied to subsurface data that show that Maiella (to the north) and Mount Alpi (to the south) belong to a continuous alignment of structural highs, developed with NNW-SSE orientation along the central-southern Apennines. South of the Maiella and Casoli tectonic windows the Adriatic-Apulia deformed Units remain buried, but other culminations appear to the south (Fig. 9) in the structural highs of Gamberale, Rionero Sannitico, and Montagnola di Frosolone (SannioMolise Units). Further south, other buried structural culminations are well marked by a series of tectonic windows of the Lagonegro Units, distributed along a NNW-SSE belt with—from north to south—Frigento, Mount Forcuso, San Fele-Bella, Mount Li Foi, Mount Volturino, Mount San Enoc, Sala Consilina, Padula, Mount Sirino-Lagonegro, and Armizzone (Fig. 9; see also Plate 2). To the SE of the Mount Sirino-Lagonegro and the Armizzone tectonic windows (Plate 2), the Apulian substratum emerges again in the Mount Alpi culmination (Fig. 16, see Ortolani and

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Figure 25. Geological map and cross section of the Colle Madonna tectonic slice (La Queglia–Colle Madonna–Teramo Unit, 12) underneath the Abruzzi and Umbria Marche Units (8), along the N-S–striking arm of the arcuate Gran Sasso overthrust (for details see Ghisetti et al., 1993b). Numbers are the same as in the legend of the Geological Map (Sheet 1). See also Figure 26.

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Figure 26. Panorama on the tectonic slice of Colle Madonna (La Queglia–Colle Madonna–Teramo Unit, 12), bounded by a set of N-S–striking, W-dipping thrust faults (in red). This large tectonic slice (see geological map and cross section in Fig. 25) deforms a calcareous succession (Eocene-Cretaceous) with “Maiolica” (12d3), “Scaglia” (12d1) and with intercalations of calcirudites (12d2 and 12d4), passing upward to the Bolognano Formation and to the Orbulina Marls (12c, Messinian-Serravallian). This succession tectonically overlies the folded lower Pliocene–postevaporitic Messinian sandstones and claystones of the Teramo Flysch (12a). In the background, masked by the vegetation, is the succession of Mount Fiore (Abruzzi and Umbria-Marche Units, 8) thrust above the Teramo Flysch (12a) and the Colle Madonna tectonic slice.

Figure 27. Panorama on the tectonic slice of the La Queglia (Unit 12), bounded by steep N-S–striking thrust faults (in red). The deformed succession comprises detrital facies of the “Scaglia Cinerea” Formation (Oligocene-Eocene, 12d), overlain by Bryozoan and Lithotamnium Calcarenites (Bolognano Formation equivalent), glauconitic sandy marls (middle-early Miocene) and Messinian-Tortonian Orbulina Marls, passing upward to the “Gessoso-Solfifera” Formation (12b) and to the Teramo Flysch (12a, early Pliocene–postevaporitic Messinian). This succession is internally deformed in a detached, tight anticline, continuous for ~4 km, with a N-S–striking axial trace plunging to the north and south, as visible on the photograph. In the background are the northwestern slope of Maiella and the Orte River Valley, carved into the Tortonian–lower Miocene Bolognano Formation (13bo), and the overlying Messinian “Gessoso-Solfifera” Formation (13 gs). The underlying Meso-Cenozoic calcareous succession in basinal facies (13pt) outcrops on the steep slopes of Maiella. The Teramo Flysch (12a) is in outcrop in the foothills, east and west of La Queglia.

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Torre, 1971; Sgrosso, 1988). The location and along-strike southward continuity of this belt of buried structural culminations is well illustrated by the contour map of the top of the ApuliaAdriatic carbonate platform (BSCSA in Sheet 1). The southernmost structural culmination is actually located in the Mount Pollino range, at the Basilicata-Calabria boundary (Fig. 9), where the contours of the buried Apulia-Adriatic carbonate platform strongly suggest that the outcropping tectonic window of Timpone Pallone, emerging from beneath the Mount Pollino and the Liguride Units (Ghisetti and Vezzani, 1982, 1983, see Fig. 30), is connected to the buried culmination of the top of the Adria carbonates, mapped by Nicolai and Gambini (2007). In the footwall of the buried thrust front of the Apulia-Adriatic deformed Units an external alignment of deeper, buried culminations of the Adria carbonates (top of the carbonates ≥ −2000 m, Nicolai and Gambini, 2007) is marked by the structural highs of Montegiordano, Rocca Imperiale and Pisticci in Basilicata (Plate 2) and of Montorio dei Frentani in Molise (Fig. 31). This outer ridge interrupts and modifies the regular flexural monocline of the buried Apulia Foreland, truncated by sets of normal faults related to later extension. The foreland becomes progressively shallower to the east, and emerges in the Gargano and Murge salients. These NNW-SSE–striking buried culminations are aligned with the ridge Frentani-Daunia Mountains, and continue southward into the Ripacandida-Stigliano-Colobraro ridge (Fig. 9). Structurally, this belt is marked by E-verging folds and thrust faults that deform the succession of the Flysch Rosso, Tufillo, Faeto, and Serra Palazzo Formations (Sannio-Molise Units), with repeated overthrusting of the Sicilide Varicolored Scaly Clays and Numidian Flysch above the Pliocene-Pleistocene deposits of the Bradanic Foredeep (cross sections 3, 5, and 10, Sheet 2). The cross sections 2, 3, 4, 5, 7, and 10 (Sheet 2) show that the deepest units of the southern Apennines are in outcrop in the

Gargano and Murge promontories (Apulia foreland) and are buried beneath the upper Pliocene–lower Pleistocene deposits of the Bradanic Foredeep, extensively exposed along the Adriatic and Ionian coast of central-southern Italy (Fig. 3). The thrust fault that separates the mildly deformed flexural monocline of the Apulia Foreland from the overlying ApuliaAdriatic deformed Units of Maiella, Casoli and Mount Alpi (Fig. 9), is locally interpreted as emerging at the surface (e.g., cross section 7 in Sheet 2), but it remains largely buried as a blind thrust, unconformably covered by the Pliocene-Pleistocene deposits of the Bradanic Foredeep. This setting is illustrated in cross section 10 (Sheet 2), east of the Colobraro ridge where the Mutignano Formation seals the overthrust of the Sicilide Units above the Molise-Sannio Units. SEQUENCE OF DEFORMATION EVENTS The sequence of shortening events in central-southern Apennines is well constrained by the time-space distribution and evolution of top-thrust basins that unconformably overlie different Apenninic imbricated units, and by the crosscutting relationships between different generations of thrust faults (Fig. 8). However, it is important to note that, (1) the stratigraphic hiatus between successions deposited in different top-thrust basins is not always well constrained by biostratigraphic data, especially where littoral to sublittoral facies are dominant, and (2) structures of the upper Miocene to upper Pliocene tectonic phases are ubiquitous and commonly obscure previous deformations. An overview of the distribution of the top-thrust marine (locally brackish) clastic successions, ranging in age from the early-middle Eocene (Albidona Formation) to the late Pliocene– early Pleistocene (Atessa Formation) is provided in Figure 5. Major points are:

Figure 28. Southern segment of the La Queglia Unit, bounded by the same N-S–striking thrust faults (in red) shown in Figure 27. This panorama illustrates the geometric setting of the eastern side of this tectonic slice where the W-dipping beds of the undifferentiated upper Miocene–Upper Cretaceous succession (12c and 12d) are thrust above the Messinian Gessoso-Solfifera Formation (12b) and the overlying sandstones and claystones of the lower Pliocene– postevaporitic–Messinian Teramo Flysch (12a, outcropping in the foreground). To the west is visible the thrust fault (in red) that superposes the Paleogene–Middle Jurassic carbonate deposits of Mount Picca (8sb, facies of scarp edge-proximal basin) onto the lower Pliocene–postevaporitic– Messinian Teramo Flysch (12a).

B

Figure 29. (A) View from north on the steep, western scarp of Maiella and Mount Porrara controlled by the N-S–striking, W-dipping Caramanico normal fault (see also Fig. 15). The Caramanico fault is one of the largest normal faults in the mapped area, exposed for a length of ~29 km. Offset increases from 2.5 to 4.2 km between Tavola Rotonda and Mount Amaro, and decreases along strike to the north, down to zero km over a distance of 25 km (see Fig. 14). In the hanging wall of the Caramanico fault is the downfaulted lower Pliocene Maiella Flysch (13f) (see cross section 2 in Sheet 2). In the fault footwall is the uplifted Meso-Cenozoic calcareous succession in carbonate platform facies of the Maiella Unit (13pt). In the foreground (Pietranico hill) are the lower Pliocene turbiditic sandstones and claystones with intercalations of polygenic breccias of the Montefino and Cellino Formations (13a). (B) West of the area of photograph A are visible the geometric relationships between the Morrone (11), La Queglia (12) and Maiella Units (13). The succession of Mount Morrone (11pt and 11ag) tectonically overlies the lower Pliocene Maiella Flysch (13f); see cross section 2 in Sheet 2. The middle-lower Pliocene conglomerates of the Mount Coppe top-thrust basin (3cc) unconformably cover the Mount Morrone carbonates (11pt), and are tectonically sliced onto the Messinian Mount Porrara Flysch (11ag). The La Queglia Unit, bounded by thrust faults to the west and to the east is tectonically interposed between the Morrone Unit in the hanging wall and the Maiella Unit in the footwall. Thrusting controls the complex relationships between different terms, as the lower Pliocene–Messinian Teramo Flysch (12a), the La Queglia Flysch, the Gessoso-Solfifera Formation (12b), and the calcareous succession in Maiolica and Scaglia facies (12d). Photograph by Paolo Barrasso. (C) Geological map of the area illustrated in photographs A and B. Colors and labels are the same as in the Geological Map (Sheet 1).

C

A

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(1) The successions pertaining to different top-thrust basins are generally distributed in regular, subparallel NW-SE–trending belts. (2) The age of the successions infilling the top-thrust basins is progressively younger from WSW to ENE, and the location of the basins shifted in time from WSW to ENE. The only exception is the youngest Atessa Formation (3aa) resting unconformably above different terms of the older Mount Coppe succession (3ca), only. (3) Some successions have a continuous, along-strike regional distribution in the whole mapped area, but others are more discontinuous or localized in narrow regions, as, e.g., the lower Pliocene?–Messinian Mts. Frentani Clastic-Evaporitic Succession (3dg). The successions of the top-thrust basin seal the thrust faults that superpose different imbricate units (Fig. 4): (a) Atessa Formation (3aa) above the Mount Coppe succession (3ca) and the Sicilide Varicolored Scaly Clays; (b) Castilenti Formation (3ba) above different horizons of the Montefino and Cellino Formations; (c) Mount Coppe Formation (3ca) above the top-thrust basins 3ds (Sandstones of Valli), 3ea (Gorgoglione Flysch) and all the underlying units (Calabride and Liguride Units excluded); (d) Gorgoglione Flysch (3ea) above the Albidona Formation (3fa) and above different formations of the Sicilide, Liguride, and, more rarely, Sannio-Molise Units; and (e) Albidona Formation (3fa) transgressive above the eo-meso-Alpine contractional structures that deform the Cretaceous-Paleogene Liguride and Calabride Units.

The superposition of allochthonous units within the thrust belt, coupled to the age of the top-thrust basins sealing the thrust contacts between imbricated units (Figs. 4 and 8) allow to reconstruct and constrain age and kinematics of the following sequence of deformation events (Fig. 31). Tectonic Phase 1 (Paleogene) The latest Cretaceous-Paleogene deformation consists in the W-verging translation of the Liguride Units against the European margin (Fig. 2), with involvement of the Frido Unit, with the ophiolitic suites in blueschist-facies and the tectonic slices of the crystalline Calabride basement (Spadea, 1982; Bonardi et al., 1988a; Knott, 1994), exposed in the Episcopia Mélange, along the Sinni River (Figs. 6 and 31). These early deformations were followed by the eastward migration and overthrusting of the imbricated Liguride and Calabride Units during the progressive shortening of the Paleogene Alpine chain (e.g., Monaco and Tortorici, 1995; Grasso, 2001). At this stage the Albidona Formation was the syntectonic infilling of the late Paleogene topthrust-foredeep basin systems. The Albidona Formation seals the eo-meso-Alpine compressional structures of the Calabride and Liguride thrust belt, and rests unconformably above the Liguride Paleogene to Upper Cretaceous Saraceno Formation (Fig. 6). The Eocene age of the Albidona Formation (Pavan and Pirini, 1963; Mostardini et al., 1966; Vezzani, 1966, 1970; Baruffini et al., 2000) constrains the chronology of this tectonic phase.

Figure 30. Cross section across the Mount Pollino area, at the Calabria-Basilicata border. The Timpone Pallone tectonic window is close to a buried structural high of the Apulia-Adriatic deformed Units (see Fig. 9 and “Buried Structure of the Central-Southern Apennines” in Sheet 1). The succession of Timpone Pallone Unit emerges from the Liguride (6), Pollino (7pc) and Verbicaro (7dv) Units, suggesting its pertinence to a structural high of the Apulia-Adriatic deformed Units. See text for a discussion. (Modified after Ghisetti and Vezzani, 1983).

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Figure 31. Structural map of the central-southern Apennines, providing an overview of the progressive involvement of the top-thrust basins and of different tectonic units (with their siliciclastic cover) into the eastward-migrating Apenninic fold-and-thrust belt. Time progression of deformation (with reference to tectonic phases described in the text) is indicated by the color coding of thrust faults of progressively younger age from Tectonic Phase 1 (Paleogene) to Tectonic Phase 6 (late Pliocene–early Pleistocene) from west to east. Compare the present position of the buried thrust front with the contractional structures affecting the Apulia-Adriatic deformed Units, represented in the “Buried Structure of the CentralSouthern Apennines” in Sheet 1. Note also the confinement of the superposed extensional faults in the western, innermost domains.

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Tectonic Phase 2 (Early-Middle Miocene) This stage is recorded by a post–Langhian-Burdigalian deformation of the Campania-Lucania platform, documented by the overthrusting of the Verbicaro Unit above the Cerchiara di Calabria Formation (Langhian-Burdigalian) pertaining to the Mount Pollino Unit (Fig. 30; see also Ghisetti and Vezzani, 1982, 1983). During this stage the innermost imbricates of the Paleogene Alpine chain of tectonic phase 1 (Calabride and Liguride Units) were transported above the already deformed lower Miocene succession of the Campania-Lucania Units. The Numidian Flysch (Langhian-Burdigalian), consisting of mature quartzarenitic turbidites of cratonic (North African) provenance (Ogniben, 1960, 1969; Wezel, 1970), was deposited on top of the Sicilide, Lagonegro-Sannio, and Sannio-Molise successions and on the back-bulge of the Campania-Lucania platform (e.g., Patacca et al., 1992a; Sgrosso, 1998; Critelli, 1999). The Sicilide Units were transported above the Albidona Formation that sealed the previously imbricated Liguride wedge in the inner sectors (Fig. 31; cross section 9 in Sheet 2) and above the Lagonegro-Sannio and Sannio Molise Units in the outermost sectors. This belt was unconformably covered during the middle Miocene by the Gorgoglione Flysch that seals: (1) intra-Liguride thrust faults and the Episcopia Mélange along the Sinni River Valley; (2) intra-Sicilide thrust faults (Mount Caldarosa, Laurenzana); and (3) thrust faults superposing the Sicilide Units above the Albidona Formation at Oriolo (Fig. 32). These relationships constrain the Sicilide overthrusting to pre–TortonianSerravallian-Langhian (?) times (age of the Gorgoglione Flysch). The occurrence of thick olistostromes with huge olistoliths of Mesozoic carbonate platform rocks (Pescatore et al., 1970; Critelli and Le Pera, 1995; Critelli, 1999) in the basal part of the Gorgoglione (Castelvetere) clastic succession records the Langhian to Tortonian involvement of the Campania-Lucania Units in the thrust belt (Critelli, 1999). To this phase is probably associated the tectonic denudation of the Lagonegro Units, through detachments along a series of layer-parallel shears at the top of the Galestri Formation, that were removed from their substratum (Fig. 11) and pushed in a more external position. Components of gravitative sliding were probably involved in these mechanisms, and triggered by the large-scale doming of the underlying Apulia-Adriatic deformed Units. This doming, accommodated by normal faults (see cross sections 7 and 8 in Sheet 2) and thrust faults (cross sections 4, 5, and 6 in Sheet 2) forced the anticlinal folding of the overlying Lagonegro Units (Menardi Noguera and Rea, 2000). Tectonic Phase 3 (Late Tortonian–Early Messinian) During the late Tortonian–early Messinian a sequence of contractional events involved the Campania-Lucania carbonate platform and the overlying Sicilide Units. These deformations substantially modified (or even reverted) the order of tectonic superposition of the previous (middle Miocene) tectonic phase

2, as shown by the superposition of the Varicolored Scaly Clays above the late Tortonian Frosinone Flysch in the area of Rio Torto and San Ambrogio Garigliano (Sheet 1). The more internal thrust fault active during this phase (Lepini-Ausoni-Aurunci Mountains overthrust) is partly included in the southwestern corner of Sheet 1 (right bank of the Liri River), along the short segment Ceccano-Rocca d’Evandro (see Plate 1). This WNW-ESE thrust fault dips at low angle (see the lobate pattern on the map and the presence of isolated klippen) and superposes the Mesozoic carbonates of the Lazio-Abruzzi platform above the Sicilide Varicolored Scaly Clays (Fig. 31). The northwestern edge of the thrust fault disappears to the north of Ceccano beneath the Roccamonfina volcanic edifice (Pleistocene). The age of thrusting is post–late Tortonian (i.e., the age of the Frosinone Flysch). Other post–late Tortonian thrust faults caused the superposition of the Campania-Lucania Units above the Sicilide Varicolored Scaly Clays and above the top-thrust basin of the Gorgoglione Flysch. These thrust faults are mapped in the high Ofanto Valley between Mount Marzano and San Fele (cross section 5, Sheet 2) and in the klippe of Mount Moschiaturo above the Pietraroja Flysch (Messinian–late Tortonian; see Vezzani et al., 2004; Festa et al., 2006, 2010a, 2010b). Moreover, post-Tortonian shortening events (Critelli, 1999) are documented by slices and precursory olistostromes of Sicilide Varicolored Scaly Clays interposed in the upper part of the Gorgoglione clastic succession (3ea), in the core of the Castelmezzano–Mount Tavernaro syncline (Sheet 2). A number of tectonic structures were active during the early Messinian (Fig. 31) as, e.g.: (1) the NW-SE frontal thrust of Cantari-Simbruini Mountains that superposes the carbonates of the Lazio-Abruzzi platform above the upper Tortonian– Messinian Val Roveto Flysch; and (2) the E-W frontal thrust of Mount Cairo–Mount Matese superposing the carbonates of the Lazio-Abruzzi platform above the lower Messinian–Tortonian Frosolone Formation and the Sant’Elena Flysch. Sets of NW-SE–oriented, doubly verging thrust faults (often with small displacement) separate the Molise Units relative to the Sicilide Units (Fig. 31) along an eastern belt continuous from the southern Abruzzi (Frentani Mountains) to northern Calabria (Ripacandida-Stigliano-Colobraro ridge). The geometry of some of these low-angle thrust faults and associated folds (with prevailing NE vergence) is portrayed in the cross sections 3, 4, 5, 7, and 10 (Sheet 2). The deformation affecting the Molise Units is typically characterized by subvertical thrust faults, associated with gravitative detachments (e.g., anticlines of Oliveto Lucano and Colobraro; see cross sections 7 and 10 in Sheet 2; see also Plate 2). Locally, the Molise Units are imbricated in a series of monoclinal slices bounded by high-angle (e.g., cross section 5, close to Ripacandida, Sheet 2; see also Plate 2) and low-angle thrust faults, verging toward the Apulia Foreland (e.g., cross section 3 between Trivento and Lentella, Sheet 1). In other localities the most continuous structures are slightly asymmetric E-verging folds with

Geology and Tectonic Evolution of the Central-Southern Apennines, Italy

Figure 32. Geological map and cross section of the Oriolo area (Calabria-Basilicata border), showing the discordant superposition of the top-thrust basins of Albidona (3fa, Langhian–Burdigalian?–Oligocene–middle-early Eocene), Gorgoglione (3ea, Tortonian-Serravallian-Langhian?) and Craco-Stigliano (3ca, middle-early Pliocene). The map and the cross section also show the discordant superposition of the Pleistocene sands and conglomerates of Arma di Lettieri (2sc) that link the Adriatic-Bradanic Foredeep to the San Arcangelo Basin. See text for a discussion (Modified after Vezzani, 1967b).

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high-angle axial surfaces, crosscut by low-angle thrust faults (e.g., Mount Castello and Orsara di Puglia; see cross section 4 in the northeastern part of Sheet 2; see also Plate 2). At the same contractional episode is also ascribed the subhorizontal thrust fault that bounds the klippe of Montenero Valcocchiara, the northern front of the Montagnola di Frosolone and the belt of small klippen that superpose the Cretaceous-Tertiary horizons of the Molise Units above their original stratigraphic cover (the lower Messinian Agnone Flysch) in the Upper Sangro River Valley (e.g., Mount Secine, Mount Campo, Mount Capraro, Mount Pagano, to the ESE of the Maiella, in Plate 1). Messinian evaporites of the Mount Castello top-thrust basin (see Matano et al., 2005) onlap the already folded Molise Units, and provide a further chronological constraint for this lower Messinian tectonic phase (cross section 4 in Sheet 2). Tectonic Phase 4 (Late Messinian–Early Pliocene) Contractional deformations of late Messinian to basal early Pliocene ? age (Fig. 31) are represented by the Meta, Genzana, and Morrone thrust fronts, as well as by the E-W Gran Sasso thrust front (Ghisetti and Vezzani, 1986a, 1991, 1997; Ghisetti et al., 1993b), the NE-SW Sibillini thrust front (Festa, 1999, 2002), and the N-S Montagna dei Fiori-Montagnone thrust front (Fig. 33). These regional tectonic thrust fronts cut the Messinian foredeep successions (Laga Flysch, 8a; Gran Sasso, Tossicia, Rocca Pia, and Scontrone Flysch, 8aa; Mount Porrara Flysch, 11a). In all these areas, folds, thrust faults and strike-slip faults display strong tectonic interference of noncoaxial trends, associated with backthrusts (e.g., Mount Gorzano and Mount Corvo), probably induced by buttressing against rigid indenters (Ghisetti and Vezzani, 1997, 2000; Festa, 1999, 2002, 2005). One of the best examples is the E-W Gran Sasso overthrust that truncates

in its footwall the N-S imbricates of the Umbria-Marche Units (Figs. 21 and 24). The overlap of discordant structural trends, common in the Lazio-Abruzzi region (cf. Ghisetti and Vezzani, 1991, 1997) and in the southern Apennines, defies the model of the regular thrust propagation from the inner to the outer zones, as proposed, e.g., by Bally et al. (1986) and Mostardini and Merlini (1986). In fact, the chronology of deformation derived from the geometry of the imbricates and the age of the syntectonic deposits suggest the repeated reactivation of thrust faults located in different position, resulting in the contemporaneous shortening of nonadjacent domains. An example is provided by the low-angle basal overthrust of the Meta Unit that deflects from N-S to ESE-WNW trends, in the area between Castelnuovo a Volturno and Civitella Alfedena, and superposes the Meta Mountains carbonates onto the Messinian siliciclastic cover of three different units: the Outer Abruzzi Units (11ag), the Abruzzi and Umbria-Marche Units (8aa), and the Lazio-Abruzzi and Campania-Lucania Units (7a). Other thrust faults active during the late Messinian are the NNW-SSE thrust faults of Passo del Diavolo, Gioia Vecchio and Mount Ventrino in the National Park of Abruzzi (Fig. 31), all causing significant internal shortening between the platform carbonate succession and the Messinian syntectonic siliciclastic deposits of the Anversa degli Abruzzi Flysch (7a) of LazioAbruzzi Units, probably associated with transpressive belts (e.g., double verging tectonic wedges of San Sebastiano along the Giovenco River in Sheet 1). Tectonic Phase 5 (Early-Middle Pliocene) In the Abruzzi region (Sheet 1) early-middle Pliocene shortening is documented by two major N-S–striking thrust faults dipping 45° W, and continuous for ~70 km from Civitella del Tronto,

Figure 33. Panorama on the Montagna dei Fiori thrust front. In the background is the Meso-Cenozoic proximal basin succession of the Abruzzi-UmbriaMarche Units (8sb), deformed by a NNW-SSE–striking anticline whose eastern, overturned limb is truncated upsection by the thrust fault T1. In the footwall are the middle-lower Miocene Orbulina Marls, the “Marne con Cerrogna” and “Bisciaro” Formations (8bc), tectonically transported (along the thrust fault T2) above the Messinian Gran Sasso Flysch (8aa). In the foreground (partially masked by the light fogs in the valley) is the NNW-SSE–striking thrust fault (T3) that superposes the Messinian Gran Sasso Flysch (8aa) onto the lower Pliocene–postevaporitic–Messinian Teramo Flysch (12a) of the La Queglia– Colle Madonna–Teramo Unit.

Geology and Tectonic Evolution of the Central-Southern Apennines, Italy to the north to Tocco da Casauria in the Pescara River Valley, to the south (Fig. 31). These thrust faults imbricate the Messinian Laga Flysch above the lower Pliocene–postevaporitic Messinian Teramo Flysch, and the latter above the lower Pliocene Montefino and Cellino Formations (cross section 1, Sheet 2). South of the Pescara River Valley, the Sicilide Varicolored Scaly Clays overlie the lower Pliocene Torrente Lajo Flysch at the top of the Casoli tectonic window along low-angle thrust faults that were subsequently folded (cross section 2 in Sheet 2; Fig. 17). Other structures formed during this stage are the thrust faults that superpose the Maiella Flysch (13f) above the Sicilide Units (4av) north of Taranta Peligna (Fig. 34; see also cross section 2 in Sheet 2) and the thrust fault that superposes the Molise Units (10d1) onto the Mount Porrara Flysch (Messinian) and the Maiella Flysch (early Pliocene), south of Taranta Peligna (Fig. 34). To the same phase belongs the set of NW-SE thrust faults exposed from Abruzzi to Lucania along the outer belt FrentaniDaunia-Ripacandida-Stigliano-Colobraro ridge (Figs. 9 and 32). These thrust faults superpose the Sicilide Varicolored Scaly Clays and the Molise Miocene succession (Faeto Formation and Numidian Flysch) onto the lower-middle Pliocene clastic deposits of the Mount Coppe-Craco top-thrust basins (e.g., cross section 3 between Lentella and San Salvo; cross section 4 east of Orsara di Puglia; cross section 7 west and east of Oliveto Lucano in Sheet 2; see also Plate 2). In Puglia along the same structural alignment (areas of Bovino, Orsara di Puglia, Panni, San Agata di Puglia at the boundary between Sheets 1 and 2; see Figs. 18 and 31 and Plate 2), early Pliocene contraction is documented by a set of NW-SE folds that deform the Faeto Formation and the overlying top-

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thrust succession of Mount Coppe-Craco conglomerates, grading upward to marly clays (3ca) of early-middle Pliocene age. In the outermost zones of Basilicata (Sheet 2), thrust faults of early Pliocene age (Fig. 31) are exposed in the area of Timpa Petrolla and Cozzo Iazzitelli, where they deform the succession of the Craco-Stigliano (3ca) top-thrust basin (early-middle Pliocene). The contractional structures of the Gorgoglione Flysch (3ea) are sealed by the lower-middle Pliocene sediments of the CracoStigliano top-thrust basin (3ca), as documented in the Mount Sodano–Arma di Lettieri syncline, northwest of Oriolo (Fig. 32). Tectonic Phase 6 (Late Pliocene–Early Pleistocene) The whole thrust belt was intensely shortened during this episode, with development of regional structures that are described in the following. In the southern regions (Sheet 2) further tectonic translation of the Sannio-Molise Units was halted against the outermost alignment of buried structural highs of the Apulia-Adriatic deformed Units (Pisticci, Rocca Imperiale, and Montegiordano in Fig. 31; see also BSCSA in Sheet 1). This buttressing was reinforced by the overall shallowing up of the Bradanic substratum toward the Apulia Foreland. The outer structural belt of the Sannio-Molise Units (Frentani-Daunia-Ripacandida-Stigliano-Colobraro ridge in Fig. 9) is characterized by strong uplift, associated with a system of NW-SE–trending, E-verging anticlines, truncated on their eastern flank by thrust faults with relevant displacements, that transport the Sannio-Molise Units above the upper Pliocene–lower Pleistocene claystones of the Adriatic-Bradanic Foredeep.

Figure 34. Eastern flank of the Maiella anticline (Unit 13), cut by the Taranta River Valley. The deep gorge exposes the gradual transition from gently E-dipping beds (at the valley head) to steeply dipping beds at the base of the calcareous scarp. The morphological scarp is controlled by the 60°–70° eastward dip of the calcareous succession, with the thick beds of the Tortonian–lower Miocene Bolognano Formation (13bo) discordant above the Santo Spirito Formation (Oligocene-Paleocene) and the Orfento Formation (Late Cretaceous), both included in the undifferentiated 13pt succession (Fig. 8). At the boundary between the Messinian (13gs) and the lower Pliocene Maiella Flysch (13f) are the Palena Conglomerates (marked by the white arrows), continuous from Lama dei Peligni (north end of the photograph) to Taranta Peligna (in the foreground), and, farther to the south (outside the photograph), to Lettopalena and Palena. The Palena Conglomerates (basal part of the early Pliocene, biozone with Sphaeroidinellopsis spp.) are only 10–30 m thick (Fig. 8). They overlie the gypsiferous marls of the Messinian “Gessoso-Solfifera” Formation (13gs) and grade upward to the lower Pliocene turbidites of the Maiella Flysch (13f), outcropping in the meadows to the east. The photograph shows that the Maiella Flysch is thrust above the Molise (10a3) and Sicilide Units (4av) north of Taranta Peligna. Photograph by Cristina Accotto.

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This structural belt defines the outcropping frontal thrust of the Apenninic chain, as shown in different cross sections (e.g., east of Orsara di Puglia in cross section 4; at Serra la Croce in cross section 5; east of Oliveto Lucano in cross section 7; at Colobraro in cross section 10; see Plate 2). Folding of the SannioMolise Units postdates the early Pliocene, as testified by the age of the Mount Coppe-Craco top-thrust clastic succession (3ca), folded together with the underlying Sannio-Molise Units. The most recent episodes of deformation and uplift of the Ripacandida-Stigliano-Colobraro ridge are well defined by the discordant overlap of the Pliocene-Pleistocene Foredeep deposits (e.g., the upper Pliocene sands of Arma di Lettieri to the east of Oriolo) directly above the lower Pliocene claystones of the Craco top-thrust basin (Fig. 32). This unconformity is largely exposed along the Ripacandida-Stigliano-Colobraro ridge, and suggests that the depositional area of the San Arcangelo Basin was still linked to the Adriatic-Bradanic Foredeep in the late Pliocene. However, the San Arcangelo Basin is now separated from the Adriatic-Bradanic Foredeep by the folded and uplifted Sicilide and Sannio-Molise Units, sealed by the clastic succession of the Mount Coppe-Craco top-thrust basin (early-middle Pliocene). Thus, the Ripacandida-Stigliano-Colobraro ridge that confined the San Arcangelo Basin, and its northwards continuation in the Daunia (Puglia) and Frentani (Molise) Mountains, was deformed and uplifted in the late Pliocene–early Pleistocene (Fig. 31). The same episode of uplift is likely to control the late detachment and gravitative emplacement of the Metaponto Nappe above the lower Pleistocene–upper Pliocene foredeep successions (Ogniben, 1969; Festa et al., 2010a, 2010b). The buried thrust front extends along the outermost parts of the Adriatic-Bradanic Foredeep, from the Ionian coast of Basilicata to the Adriatic coast of Molise and Abruzzi (Fig. 31).

The progressive eastward translation of the imbricates of the Frentani-Daunia-Ripacandida-Stigliano-Colobraro ridge is marked by the final overthrusting of the Sannio-Molise and Sicilide Units above the upper Pliocene deposits of the AdriaticBradanic Foredeep (Figs. 18 and 31). The overlying San Arcangelo Basin, linked to the Bradanic Foredeep till the late Pliocene, was passively transported to the east on top of the allochthonous Sannio-Molise Units, and thus can be considered as the youngest top-thrust basin in the area of Sheet 2. In the northern areas of Abruzzi and Molise the Frentani Tectonic Mélange (Vezzani et al., 2004; Festa et al., 2006, 2010a, 2010b) is the outcropping equivalent of the Metaponto Nappe. The overthrust of this mélange above the late Pliocene bluish marly clays of the Adriatic-Bradanic Foredeep is well exposed on the right bank of the Trigno River, south of San Salvo (Fig. 35). This tectono-sedimentary mélange is formed by a prevailing matrix of chaotic varicolored scaly clays enclosing blocks (1–10 m in diameter) of lower Miocene marly limestones and calcarenites, Tortonian marls, Messinian gypsiferous evaporites and bluish claystones of the Plio-Pleistocene foredeep. Seismic data and drillings (cross section 3 in Sheet 2) document the subsurface development of this allochthonous body, which extends as far as the Adriatic coast from the Abruzzi till to the Ionian Sea in Basilicata (see continuity of this buried thrust front in Fig. 31). EXTENSIONAL FAULTS SUPERPOSED ONTO THE CONTRACTIONAL EDIFICE From the inner to the outer zones of the Apennines there are strong differences in terms of crustal thickness, heat flow, volcanism, tectonic foundering, uplift rates and seismicity. Crustal thinning, involving seismogenic normal faulting and concurrent volcanic activity are all evidence of postcollisional extensional

Figure 35. Thrust fault (in red) on the right bank of the Trigno River (Masseria Palumbo). This fault dips 15° SSW and superposes the Varicolored Scaly Clays (4av, Sicilide Units) onto the lower Pleistocene–upper Pliocene bluish marly clays of the Mutignano Formation (2a). The Varicolored Scaly Clays display a block-in-matrix structure with metric to decametric blocks (indicated by white arrows) of lower Miocene calcarenites, Tortonian marls and Messinian gypsiferous evaporites, enveloped in a scaly clay matrix. This thrust fault, with a flat-ramp geometry, is an emerging splay of the buried thrust front bounding at the base the Frentani Tectonic Mélange (Festa et al., 2006).

Geology and Tectonic Evolution of the Central-Southern Apennines, Italy collapse of the Apenninic thrust belt, associated with progressive growth and migration of extensional faults across the contractional edifice. Many authors have observed the contemporaneous occurrence of contractional and extensional deformations at different structural levels in the Apennines (e.g., Elter et al., 1975; Scandone, 1979; Malinverno and Ryan, 1986; Savelli, 1988; Carmignani and Kligfield, 1990; Patacca et al., 1990; Doglioni, 1995; Ghisetti and Vezzani, 1995, 1999, 2002a, 2002b; Frepoli and Amato, 1997; Boccaletti and Sani, 1998). Possible mechanisms driving horizontal extension in actively converging deforming belts are: (1) re-equilibration of the deformed accretionary wedge (Dahlen et al., 1984; Wallis et al., 1993); (2) passive retreat of the subducted slab (Waschbusch and Beaumont, 1996); and (3) gravitational collapse of overthickened crust (England and Molnar, 1991). These different interpretations have been proposed by various authors (e.g., Locardi, 1988; Channell and Mareschal, 1989; Doglioni et al., 1996; Faccenna et al., 1997; Barchi et al., 1998; Decandia et al., 1998). The Apennines as a whole (Fig. 1), and the central-southern Apenninic belt in particular provide a detailed syntectonic sedimentary record of the time-space migration of the contractional and extensional structures from the hinterland to the foreland, correlated to regional variations in topography across the chain (Mazzanti and Trevisan, 1978; Alvarez, 1999; Ghisetti and Vezzani, 1999, 2002a). The complex interplay of thrusting, normal faulting, and erosion affects the exhumation history, determining rates of uplift and basin formation (Ring et al., 1999). Figure 36 defines four major tectonic domains, in terms of: (1) lithospheric thickness; (2) changing orientation of the stress field from the inner extensional domains to the outer compressional domains (Ghisetti and Vezzani, 1981; Amato and Montone, 1997; Frepoli and Amato, 1997); and (3) progressive eastward migration of extension resulting in the progressive disruption and foundering of the thrust belt. Stretching and crustal thinning of the Tyrrhenian crust are intense south of latitude 41° N. Collapse of the inner margin of the thrust belt by regional extensional downfaulting (Figs. 1 and 3) is documented by stratigraphic-structural data that demonstrate progressive eastward migration of the extensional front behind the similarly migrating compressional front (Elter et al., 1975; Malinverno and Ryan, 1986; Carmignani and Kligfield, 1990; Patacca et al., 1990; Boccaletti and Sani, 1998; Ghisetti and Vezzani, 1995, 1999, 2002a; Frepoli and Amato, 1997; D’Agostino et al., 2009). The development of normal faults since the late Tortonian– Messinian (Patacca et al., 1990) appears to have occurred in a stress field where the axis of maximum horizontal extension remained coaxial relative to the axis of maximum horizontal compression in the thrust belt. Negative inversion from compression to extension is probably triggered by strong components of uplift following shortening and thickening of the imbricate wedge, requiring null differential stress at the transition from compression to extension.

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The chronological onset of E-younging extensional basins and of contemporaneous top-thrust basins transported above E-verging thrust sheets shows that the contractional and extensional fronts advanced at similar rates of ~4 cm/yr (Fig. 37), consistent with the model of back-arc extension of the Tyrrhenian Basin in front of the eastward-retreating Adriatic slab (Ghisetti and Vezzani, 2002b). The time lag of the onset of extension relative to the already formed contractional structures controls the present position of the front of Tyrrhenian crustal stretching relative to the outer thrust front, resulting in the development of longitudinal belts with different amounts of extensional overprinting onto the contractional wedge (Figs. 3 and 36), as well as distinct styles of seismicity and characters of the Quaternary magmatism (Fig. 36) (Cavinato and De Celles, 1999; Ghisetti and Vezzani, 1999, 2002b; Carminati et al., 2004). The present front of extension lies close to the orographic divide, which is also the boundary between western zones with significant finite extension and eastern zones with minor components of superposed extension (Figs. 3 and 36). This relationship indicates that the rapid, post–7 Ma extensional collapse of the stretched Tyrrhenian and peri-Tyrrhenian crust exerts a strong morphotectonic control. In fact, structural and morphotectonic analyses in the central Apennines (Ghisetti and Vezzani, 1999) reveal that the outer axis of maximum uplift migrated to the east of the orographic divide (Fig. 37) during the middle Pliocene– early Pleistocene, in the wake of the tectonically controlled uplift (Ghisetti and Vezzani, 2002a). Geometry and Structure of the Normal Faults The normal faults of the Apennines are significant structures in terms of regional extent, finite displacement, morphotectonic signature and seismic activity (Fig. 38). In the mapped area dominant WNW-ESE (longitudinal) normal faults dip 60°–80° SSW; some notable exceptions are E-W–trending (transverse) faults (e.g., Gran Sasso, Matese, Pollino). In many cases, repeated reactivation of the normal fault systems during the Quaternary is testified by the development of terrestrial extensional basins occupying fault hanging walls. The best examples occur in the Lazio-Abruzzi and Campania-Lucania Units (e.g., Campo Imperatore, Aterno, Fucino, Sulmona, Liri Valley, Mercure, Frascineto; see Fig. 38 and Plates 1 and 2) where normal faulting of rigid carbonate platforms in elevated areas provided the best conditions for the development of large intramontane basins (see, e.g., Figs. 40 and 41). A general feature shown by the Geological Map and accompanying cross sections (Sheet 2) is that the high-angle normal faults cut across the gently W-dipping back limbs of E-verging thrust-propagation anticlines (or hanging-wall anticlines). However, most faults propagated with an orientation subparallel to slightly oblique to the thrust faults and fold axial traces. In fact, the “transverse” trend of the E-W–striking normal faults (e.g., Gran Sasso, Matese, Pollino) is only apparent,

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because the faults are in fact subparallel to thrust faults that were rotated into an E-W orientation (e.g., Dela Pierre et al., 1992). These relationships suggest a strong control exerted by the contractional structural fabric on the propagation trajectories of the normal faults. However, it is difficult to prove for each individual normal fault whether it merges into the same detachment horizon as the thrust faults, or rather crosscuts the whole imbricate stack (Fig. 36). As shown by the cross sections (in Sheet 2) it is likely that there is a wide range in penetration depths, depending on the fault’s finite displacement, slip rate, and position in the tectonic wedge. Some of the major normal faults of the central-southern Apennines are depicted in the photographs, like the ENE-WSW Mount Corvo–Tre Selle–Campo Imperatore fault (Figs. 39,

40, and 41), the E-W Mount Paradiso fault (Fig. 42), the E-W Mount San Franco fault (Fig. 43), the NW-SE Capo di Serre fault (Fig. 44), and the NNW-SSE Mount Rotella fault (Fig. 45). Other important normal faults are the N-S Mount Alpi fault (Fig. 16) and the N-S Mount Moschereto fault (Fig. 46) in the Mount Pollino range. All these faults have total displacements of a few km, but other faults with lesser amounts of displacement are also significant, because they truncate the youngest Pleistocene terraced deposits. The kinematics recorded on the striated fault surfaces is often indicative of pure or near-pure dip-slip mechanisms. Most of the largest normal faults (with total displacement >1–2 km) have slip rates of 1–2 mm/yr (calibrated over Quaternary deposits; cf. Westaway, 1992; Vezzani and Ghisetti, 1998; Ghisetti et al., 2001).

Figure 36. (A) Tectonic setting of the Apenninic chain related to asthenospheric wedging in front of the retreating Adriatic plate, and consequent extensional stretching of the Tyrrhenian hinterland and active shortening in the outer Adriatic zones (see Doglioni, 1991; Doglioni et al., 1996). (B) Cross section from the Tyrrhenian Sea to the Adriatic Sea (Latina-Ortona, see trace in Fig. 37) illustrating differences of geometry and depth of detachment of normal faults and changes of regional topographic gradient, as related to different deformation regimes from the hinterland to the foreland. The crustal section highlights the connections between deep and upper crustal deformations and the structural control on decreasing permeability and fluid mixing from the innermost domain 1 (stretched, highly permeable crust) to the outermost domain 4 (shortened, overpressured crust with restricted fluid circulation). Note the change in vertical scale above and below sea level. See also Figure 3. The belt of highest seismicity (see also Fig. 48) is located in between domains 2 and 3, where mature normal faults cut across the brittle crust (after Ghisetti and Vezzani, 2002b). Crustal depth of the Moho and of the intermediate crustal discontinuity is after Scarascia et al. (1998). Mature normal faults in the Tyrrhenian hinterland are depicted with listric geometry, penetrate the crust down to the intermediate crustal discontinuity, and cause collapse and thinning of the upper crust. In contrast, east of the orographic divide, the normal faults rotate into listric geometry at the depth of the basal detachment horizon (Late Triassic Burano anhydrites).

Geology and Tectonic Evolution of the Central-Southern Apennines, Italy

A

B Figure 37. (A) Regional map illustrating the present position of the Sicilide and Liguride Units in relation to the distribution of the top-thrust basins, the position of the orographic divide, and the location and extent of the zone of maximum uplift and denudation since the middle Pliocene (modified after Ghisetti and Vezzani, 1999). A–B is the trace of the crustal cross section of Figure 36; (B) ideal transect illustrating the time migration of extension and compression since 7 Ma from the innermost (light blue) to the outermost (gray) tectonic domains. Note that extension and shortening have migrated at comparable rates (~4 cm/yr), and that extension of the thrust belt east of the orographic divide is relatively young (<3 Ma). Color code is the same as in Figure 3. (Modified after Ghisetti and Vezzani, 2002b).

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Figure 38. Regional location and geometry of the major normal faults superposed onto the thrust belt of the central-southern Apennines (see also Figures 3, 36, 37 for the extent of the downfaulted domains in the thrust belt, and Figure 48 for the relationships with seismicity). Note the distribution of the Quaternary intramontane basins bounded by normal faults, and the linking between the normal faults and the elevated structural highs of the Apulia-Adriatic deformed Units (see also Fig. 9). The buried normal faults are after Nicolai and Gambini (2007).

Geology and Tectonic Evolution of the Central-Southern Apennines, Italy

Figure 39. Western segment of the Tre Selle normal fault (in red) truncating the south flank of Mount Corvo, along the Chiarino River valley. This fault is part of a regional E-W system, developed at the back of the Gran Sasso–Mount Corvo thrust front. Here the fault plane dips 75°–85° S and uplifts the “Maiolica” and “Scaglia” Formations (Eocene-Cretaceous) in the footwall (8sb) relative to the Tortonian “Marne con Cerrogna” Formation (8bc) in the hanging wall. Total offset is ~1 km, and decreases westward.

Figure 40. Western segment of the Vado di Corno normal fault (in red), at the rear of the Gran Sasso thrust front. View from Mount Aquila. On the left-hand side is the southern slope of the Mount Brancastello– Mount Prena–Mount Camicia ridge (the northern slope of the same ridge is illustrated in Figures 23 and 24), truncated by the Vado di Corno normal fault, with development of a thick belt of cataclasites and gouges that disrupt dolomitic and calciruditic units (bright white belt in the photograph). The fault dips 55°–70° S, and bounds the elevated intramontane basin of Campo Imperatore (see 1 in Fig. 38), filled with Quaternary moraines and fluvio-glacial deposits (1g) and with alluvial fans. Overall displacement is >1.5 km, with offset of the youngest alluvial fans and terraces (Carraro and Giardino, 1992). The southern margin of the Campo Imperatore basin is bounded by the ridge of the Scindarella Mountains, dissected by large glacial circuses.

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Figure 41. Central segment of the Vado di Corno normal fault (in red), east of the segment illustrated in Figure 40. View from Coppe di Santo Stefano. The Vado di Corno fault truncates the Gran Sasso Units from Mount Brancastello to Mount Prena and bounds the intramontane basin of Campo Imperatore, filled with terraced deposits (1t) and alluvial fans (Holocene–late Pleistocene). A thick belt of cataclasites and gouges (the same belt shown in Fig. 40) is developed along the fault. In the footwall of the fault, the sharp boundary between the vegetated and unvegetated slope (marked by the red line with triangles) is the trace of the E-W–striking low-angle thrust fault that superposes the Mount Prena “Calcare Massiccio” (7pc) above the folded Mesozoic-Tertiary proximal basin succession of the Abruzzi and Umbria-Marche Units (8sb). The same thrust fault is exposed on the north slope of Mount Camicia and Mount Prena, as illustrated in Figures 22, 23, and 24. Comparison between this figure and Figures 23 and 24 also shows the strong morphological contrast between the south slope of the Gran Sasso thrust belt (with an elevation drop of nearly 1000 m) and the north slope, with an elevation drop of ~2000 m. Photograph by Marco Giardino.

Figure 42. Panorama of Mount Paradiso, at the southern border of the Campo Imperatore intramontane basin. Mount Prena and Mount Camicia are in the background. At the base of the Mount Paradiso scarp a WNW-ESE–striking normal fault (in red) truncates the middle-lower Pliocene conglomerates of Mount Coppe top-thrust basin (3cc) and the underlying Rudistid Calcirudites of the carbonate proximal basin succession of the Abruzzi and Umbria-Marche Units (8sb). Pleistocene uplift is suggested by the E-W morphological scarp (with trapezoidal facets) in terraced terrestrial deposits (1t), in the foreground.

Geology and Tectonic Evolution of the Central-Southern Apennines, Italy

Figure 43. Along-strike view of the striated surface of the NW-SE–striking Mount San Franco normal fault. This fault is subparallel to the Tre Selle normal fault, that extends from Mount Corvo (Fig. 39) to Vado di Corno (Fig. 40) and to Campo Imperatore (Figs. 41 and 42). The fault dips 70°–80° S, and upthrows the “Maiolica” Formation (Early Cretaceous–Malm) in the footwall relative to the Cerrogna Marls (8bc, middle-early Miocene) and the Messinian Gran Sasso Flysch (8aa), in the hanging wall, with a total offset of ~700 m. Thick belts of cataclasites and gouges are locally developed along the fault.

Figure 44. Striated, steep fault plane of the NW-SE Capo di Serre normal fault with dolomitic limestones in the footwall. This fault (like many other major normal faults crosscutting the rigid carbonates of the Abruzzi Units) is characterized by a distinct zoning of mesostructures, from the intact host rock in the footwall farthest from the fault to the intensely brecciated and cataclastic belt of the principal slip zone (See Fig. 47).

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Figure 45. Southern segment of the W-dipping Mount Rotella–Rivisondoli normal fault that truncates to the west the Outer Abruzzi Units. View from south. Repeated seismic activity of this fault during the Quaternary is documented by paleoseismic studies (Calderoni et al., 1990). In outcrop the fault dips 50°–80° to the WSW. In the foothills is visible the thrust fault that superposes the Mesozoic carbonate deposits in facies of platform scarp edge-proximal basin of the Mount Genzana Unit (8sb) above the Cretaceous–upper Lias carbonate platform deposits of Mount Rotella (11pt). In the foreground are the Pleistocene fluvial-lacustrine deposits (1t) infilling the extensional depression of “Piano delle Cinque Miglia.”

Figure 46. Mount Moschereto normal fault in the Pollino Range (see Ghisetti and Vezzani, 1982, 1983). This N-S– to NW-SE–striking normal fault dips 75°–80° E and uplifts the Jurassic-Triassic carbonate succession of the Timpone Pallone Unit (in the footwall) relative to the lower Miocene formations of the Pollino Unit (in the hanging wall) with an overall displacement of ~1.5 km (see Fig. 30). The fault is marked by a thick belt of cataclasites and cemented gouges along a continuous (~5 km) striated fault plane that controls a prominent morphological scarp.

Geology and Tectonic Evolution of the Central-Southern Apennines, Italy Fault zones are often marked by cataclastic belts (with thicknesses ranging between tens to hundreds of meters) that display a marked zoning, with increase in fracture intensity, grain-size reduction, and cementation toward the slip surface (Fig. 47). Depth of penetration of the normal faults decreases from west to east in agreement with the decrease in crustal stretching and younging of the faults (Ghisetti and Vezzani, 2002b). In this interpretation, (1) normal faults of the Tyrrhenian and peri-Tyrrhenian margin with a longer history of evolution possess listric geometry, penetrate the whole crust, and detach within the crystalline basement, and (2) the youngest normal faults superposed onto the thrust belt east of the divide do not penetrate deeper than the basal detachment between the cover succession and the crystalline basement, and curve into low-angle planes at depth of ~10–13 km (Fig. 36). An apparent anomaly of this trend is found along the structural and topographic culmination of the Apulia-Adriatic deformed Units, as observed in the Maiella (e.g., the Caramanico Fault on the west flank of Maiella; see Fig. 29 and cross section 2 in Sheet 2) and at Mount Alpi (Fig. 16; see cross section 9 in Sheet 2). The elevated Maiella anticline

Figure 47. Schematic cross sections showing the zoning of fault rocks associated with the Capo di Serre normal fault. Six zones have been differentiated: 1— moderately fractured footwall rock; 2—uncemented cataclasite; 3—cemented cataclasite; 4— very fine-grained, homogeneous pink horizon; 5—cemented fine-grained cataclasite; and 6—Quaternary sediments that are locally cemented. Modified after Ghisetti et al. (2001).

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is bounded by high-angle normal faults with large total displacements and high slip rates (e.g., 2.6 mm/yr estimated for the Caramanico Fault by Ghisetti and Vezzani, 1999, 2002a). However, these normal faults are steep, and cannot contribute greatly to regional extension. In the external zones rapid growth and propagation of high-angle normal faults appear to accommodate uplift of the buoyant deformed Adriatic-Apulia platform along the collisional boundary between the flexed continental crust of the Apulia foreland plate and the Apenninic thrust wedge. Normal Faults and Seismicity The regional evolution of the Apenninic normal faults fits a model (e.g., Buck, 1988; King and Ellis, 1990) where the incipient stages of normal faulting are accommodated by high-angle, planar faults in the upper crust, unable to accommodate large extensional strains. With time, progressive growth and aging of these planar normal faults led to propagation of listric fault planes and block rotation, associated with increasing extensional strain and crustal stretching. Within this evolutionary trend, foreland to hinterland transects across the Apennines provide a time slice of the progressive evolution from young, newly generated normal faults (to the east) to progressively older and mature faults (to the west). Structural and geochemical data (Ghisetti and Vezzani, 1997, 1999, 2000; Chiodini et al., 2000; Ghisetti et al., 2000, 2001; Italiano et al., 2000) indicate that this transition leads to enhanced vertical permeability, connectivity and fluid mixing. In particular, the orographic divide (see Fig. 36) marks the boundary between (1) a western sector characterized by highly permeable crust, rich in juvenile and magmatic fluids that penetrate through a dense extensional fracture network, and (2) an eastern sector where fluid circulation is restricted to normal faults that crosscut the contractional wedge (Fig. 36). Fluid circulation is inhibited in the easternmost domain not yet affected by any relevant extension, and characterized by overpressured fluids at shallow depth, as testified by measurements in many hydrocarbon wells in the area. This evolution appears to exert an important control on the present seismicity of the Apennines (Fig. 48). Background seismicity is rather diffuse all along the Apennines, but the strongest activity is concentrated in a belt that closely follows the orographic divide, with 5 ≤ Mw ≤ 7 historical normal faulting earthquakes inferred to occur with recurrence intervals ≥1 ka (Vittori et al., 1991; Pantosti et al., 1993, 1996; Giraudi and Frezzotti, 1995). In particular the mapped area (Sheet 1) encloses the seismic faults of one of the largest and destructive historical earthquakes that affected Italy in the last century (Avezzano earthquake of 13 January 1915, Mw ~7.0; see Fig. 48) at the eastern margin of the Fucino depression (cf. Ward and Valensise, 1989). During the preparation of this paper the nearby region of the Aterno Valley (L’Aquila) was struck by a

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Figure 48. Distribution of the strongest historical earthquakes (M ≥ 5) of the central-southern Apennines attributed to active normal faulting in the upper crust, superposed onto the map of the major normal faults that dissect the contractional edifice. See text and Figure 36 for a discussion.

Geology and Tectonic Evolution of the Central-Southern Apennines, Italy Mw 6.3 earthquake (main shock on 6 April 2009) with severe damage and many fatalities in the town of L’Aquila and surrounding villages (Vezzani et al., 2009; EMERGEO Working Group, 2010). Normal fault seismicity remains confined at depth ≤10– 15 km, i.e., the maximum depth of inferred detachment for the normal faults close to the orographic divide (Fig. 36). The regional distribution of the strongest shocks (Fig. 48) suggests that transcrustal permeability and overpressuring of the crust undergoing early stages of extension exerts a strong control on the seismicity of the normal faults. In particular, the largest earthquakes are potentially triggered by conditions of overpressuring that help create new favorably oriented normal faults or allow reactivation of unfavorably oriented inherited thrust faults. The strongest seismicity is thus associated with the eastward breakthrough of the extensional front through time (Fig. 2), whereas the older normal faults left behind in the stretched, permeable and melt-intruded crust may well become reactivated, but seemingly fail to produce large earthquakes (cf. Ghisetti and Vezzani, 2002b; Vezzani et al., 2009). ACKNOWLEDGMENTS We thank W. Cavazza, D.S. Cowan, G.A. Pini, and J. Wakabayashi for their careful reviews that greatly helped in focusing and clarifying our arguments. We also thank M.E. Bickford for the editorial help and R.H. Sibson for kindly reviewing a late draft of the manuscript. We are grateful to G. Valensise and R. Basili (INGV) for providing the digital elevation model utilized in the book cover, and to Y. Dilek for his support to an early stage of preparation of the manuscript. REFERENCES CITED Accordi, B., 1966, La componente traslativa nella tettonica dell’Appennino laziale-abruzzese: Geologica Romana, v. 5, p. 355–406. Accordi, G., and Carbone, F., 1986, Lithofacies map of Latium-Abruzzi and neighbouring areas: C.N.R. Progetto Finalizzato Geodinamica, Salomone, Roma, scale 1:250,000, 1 sheet. Accordi, G., and Carbone, F., eds., 1988, Lithofacies map of Latium-Abruzzi and neighbouring areas: C.N.R., Quaderni de “La Ricerca Scientifica,” v. 114, no. 5, p. 7–215, scale 1:250,000, 1 sheet, with explanatory notes. Alvarez, W., 1976, A former continuation of the Alps: Geological Society of America Bulletin, v. 87, p. 891–896, doi: 10.1130/0016-7606(1976)87<891: AFCOTA>2.0.CO;2. Alvarez, W., 1999, Drainage on evolving fold: a study of transverse canyons in the Apennines: Basin Research, v. 11, p. 267–284, doi: 10.1046/j.1365 -2117.1999.00100.x. Amato, A., and Cimini, G.B., 2001, Deep structure from seismic tomography, in Vai, G.B., and Martini, I.P., eds., Anatomy of an Orogen: The Apennines and Adjacent Mediterranean Basins: Kluwer Academic Publishers, p. 33–46. Amato, A., and Montone, P., 1997, Present-day stress-field and active tectonics in southern peninsular Italy: Geophysical Journal International, v. 130, p. 519–534, doi: 10.1111/j.1365-246X.1997.tb05666.x. Amodio Morelli, L., Bonardi, G., Colonna, V., Dietrich, D., Giunta, G., Ippolito, F., Liguori, V., Lorenzoni, S., Paglionico, A., Perrone, V., Piccarreta, G., Russo, M., Scandone, P., Zanettin Lorenzoni, E., and Zuppetta, A., 1976,

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Section 5, Geological-Structural Map of the Central-Southern Apennines (Italy) Geological Society of America Special Paper 469 Geology and Tectonic Evolution of the Central-Southern Apennines, Italy By Livio Vezzani, Andrea Festa, and Francesca C. Ghisetti ©2010 The Geological Society of America. All rights reserved.