Late thrusting extensional collapse at the ... - Wiley Online Library

TECTONICS, VOL. 31, TC4019, doi:10.1029/2011TC003059, 2012

Late thrusting extensional collapse at the mountain front of the northern Apennines (Italy) Stefano Tavani,1,2 Fabrizio Storti,3 Jordi Bausà,2 and Josep A. Muñoz2 Received 1 November 2011; revised 15 May 2012; accepted 27 June 2012; published 14 August 2012.

[1] Thrust-related anticlines exposed at the mountain front of the Cenozoic Appenninic thrust-and-fold belt share the presence of hinterlandward dipping extensional fault zones running parallel to the hosting anticlines. These fault zones downthrow the crests and the backlimbs with displacements lower than, but comparable to, the uplift of the hosting anticline. Contrasting information feeds a debate about the relative timing between thrust-related folding and beginning of extensional faulting, since several extensional episodes, spanning from early Jurassic to Quaternary, are documented in the central and northern Apennines. Mesostructural data were collected in the frontal anticline of the Sibillini thrust sheet, the mountain front in the Umbria-Marche sector of the northern Apennines, with the aim of fully constraining the stress history recorded in the deformed multilayer. Compressional structures developed during thrust propagation and fold growth, mostly locating in the fold limbs. Extensional elements striking about perpendicular to the shortening direction developed during two distinct episodes: before fold growth, when the area deformed by outer-arc extension in the peripheral bulge, and during a late to post thrusting stage. Most of the the extensional deformation occurred during the second stage, when the syn-thrusting erosional exhumation of the structures caused the development of pervasive longitudinal extensional fracturing in the crestal sector of the growing anticline, which anticipated the subsequent widespread Quaternary extensional tectonics. Citation: Tavani, S., F. Storti, J. Bausà, and J. A. Muñoz (2012), Late thrusting extensional collapse at the mountain front of the northern Apennines (Italy), Tectonics, 31, TC4019, doi:10.1029/2011TC003059.

1. Introduction [2] The Apennines thrust-and-fold belt has long been recognized as a promising site for studies on fracture development in contractional setting [Alvarez et al., 1978; Marshak et al., 1982; Geiser, 1988; Marshak and Engelder, 1985; Storti and Salvini, 2001; Graham et al., 2003; Tondi et al., 2006; Agosta and Aydin, 2006; Antonellini et al., 2008; Tavani et al., 2008, 2010]. Despite the abundance of these studies, many debated points still exist about the macro and mesostructural deformation sequence of the belt. A major one concerns the relationships between thrusting and beginning of extensional deformations at the mountain front of the Apennines, where thrust-related anticlines uplifted of some kilometers host extensional fault zones downthrowing 1 Dipartimento di Scienze della Terra, Università degli Studi di Napoli Federico II, Napoli, Italy. 2 Geomodels, Departament de Geodinamica i Geofisica, Universitat de Barcelona, Barcelona, Spain. 3 Dipartimento di Scienze della Terra, Universitá degli Studi di Parma, Parma, Italy.

Corresponding author: S. Tavani, Dipartimento di Scienze della Terra, Università degli Studi di Napoli Federico II, Largo San Marcellino 10, I-80138 Napoli, Italy. ([email protected]) ©2012. American Geophysical Union. All Rights Reserved. 0278-7407/12/2011TC003059

the crests and the backlimbs, with displacements lower than, but comparable to, the uplift of the contractional hosting structure (Figure 1). The occurrence of several pulses of deformations in the region implies problems for the trustworthy dating of extensional deformation structures. [3] The deformation history recorded in the sedimentary successions exposed in the central and northern Apennines started in Triassic to early Jurassic times, with the Tethian rifting [Castellarin et al., 1978; Alvarez, 1990; Santantonio, 1993] and continued during the Cretaceous-Paleogene drifting stage [e.g., Tavarnelli, 1996; Marchegiani et al., 1999]. Growth of the Apennines fold-and-thrust belt, during Paleogene-Neogene times [e.g., Elter et al., 1975; Bigi et al., 1990; Patacca et al., 1990; Cavinato and DeCelles, 1999], caused extensional faults development in the foreland basin undergoing flexural bending ahead of the advancing thrust front [Calamita and Deiana, 1980; Mazzoli, 1994; Scisciani et al., 2001; Mazzoli et al., 2002]. All this inherited extensional deformation pattern was progressively involved into the orogenic belt and commonly overprinted by contractional deformation structures [Tavarnelli and Peacock, 1999]. Syn-contractional extensional faults then developed during the growth of many thrust related anticlines [Migliorini, 1948; Barchi et al., 1991; Graham et al., 2003; Patacca et al., 2008; Tavani et al., 2008] and extensional stress fields are documented in the shallower portions of

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Figure 1. (a) Structural sketch map of Italy. (b) Elevation map of central Italy with the axial traces of the more external late Miocene to Pliocene anticlines, thrusts and extensional faults; SVF = San Vicino Fault; VF = Vettore Fault. (c) Cross section of the Montagna dei Fiori anticline, modified and adapted from Mattei [1987]. (d) Cross section of the Gran Sasso anticline, modified and adapted from D’Agostino et al. [1998]. (e) Regional cross section across the Sibillini thrust sheet and adjacent foreland structures, modified and adapted from Scarselli et al. [2007]. See Figure 1b for location. more external and active thrust-related anticlines [e.g., Carminati et al., 2010]. Post-orogenic extension developed at the rear of the eastward propagating orogenic belt [e.g., Elter et al., 1975; Lavecchia et al., 1994; Storti, 1995; Cello et al., 1997; Jolivet et al., 1998; Cavinato and DeCelles, 1999; Boncio et al., 2000; Collettini et al., 2000], commonly reworking the inherited fault networks [D’Agostino

et al., 1998; De Paola et al., 2006]. This extensional stage is still active and it is associated with large earthquake activity [e.g., D’Agostino et al., 2009; Chiarabba et al., 2011], which affects the mountain front of the northern and central Apennines. However, there is no robust evidence that many extensional faults of the more external mountain front anticlines of the central Apennines are included in the

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extensional, and seismically active, domain of the Apennines. Accordingly, although at a lithospheric scale of observation it is pretty evident that most of the extensional deformation has occurred during the Quaternary stage, at the scale of single thrust sheets things become more complex. In such a longliving deformational history, in fact, it can be difficult to establish the relative chronology between thrusting and extensional faulting events, and this explains why different authors support either pre- [Scisciani et al., 2001; Calamita et al., 2011], syn- [e.g., Patacca et al., 2008], or late to post-orogenic [D’Agostino et al., 1998; Ghisetti and Vezzani, 2002] development for the main extensional fault systems occurring along the mountain front, respectively. In particular, the evidence that compressional mesostructures postdate pre-folding extensional ones [Tavarnelli and Peacock, 1999], was used to support a pre-folding origin for many large-scale normal faults [e.g., Calamita et al., 1998; Scisciani et al., 2001]. On the other hand, in many cases thrusts are crosscut by superimposed Quaternary normal faults [e.g., Calamita et al., 2000], while in other cases normal faults at the mountain front run subparallel to reverse faults and fold axial surfaces, having maximum displacements in the structural culminations of the hosting anticlines [e.g., Ghisetti and Vezzani, 2000]. Moreover, it is frequent that when contractional elements change their orientation, normal faults closely match these changes. These observations provide support to the post-contractional interpretation, where the inherited contractional topography influenced the stress configuration producing extensional faults paralleling thrusts and fold axial trends [D’Agostino et al., 1998]. However, the same observations match also an at least partial syn-folding origin, supported by geomorphological evidence indicating that many of these mountain front extensional faults were not active during the post-contractional extensional stage [Fubelli et al., 2009]. [4] In order to provide further constraints to the relative chronology of contractional and extensional deformations, a field study was carried out in the frontal anticline of the Sibillini thrust sheet, representing the mountain front in the southern part of the northern Apennines (Figures 1 and 2). This structure is characterized by the presence of extensional faults striking parallel to the frontal thrust. Their displacement is, however, lower than few hundreds of meters, leaving the geometry of the thrust-related frontal anticline well preserved. This is a crucial point for the aim of this study, as it allows us to verify whether a relationship between hosting fold attributes and embryonic extensional deformation does exist. In our investigation we took advantage of results from studies on similar map-scale contractional anticlines in other thrust and fold belts, which has recently increased the knowledge about both methodologies for mesostructural data analysis and folding related fracturing templates. In particular, pre-folding mesostructures developed both during early [Lacombe et al., 2011; Vitale et al., 2012; Quintà and Tavani, 2012] and pre-orogenic stages [e.g., Silliphant et al., 2002; Bellahsen et al., 2006a], have been increasingly recognized in thrust belts worldwide, significantly influencing the syn- to post-contractional deformation patterns (Bergbauer and Pollard, 2004; Bellahsen et al., 2006a; Tavani et al., 2011]. This, together with the documented high variability of syn-collisional stress conditions at the front of thrust belts [e.g., Bellahsen

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et al., 2006b; Evans, 2010; Beaudoin et al., 2012], can determine a wide range of early to syn-thrusting/folding deformation patterns, witnessing how the study of mesostructural assemblages in thrust related anticlines cannot be addressed by means of simple folding-related fracturing templates. More importantly, only mesostructural analysis based on robust data sets, allowing us to appreciate small but significant variations of analyzed attributes, has been proved to be a reliable tool allowing us to constrain regional scale deformation sequences, even in complex and multiphase tectonic frameworks [e.g., Tavani et al., 2011; Beaudoin et al., 2012]. [5] Analysis of about 4000 mesostructural data collected in the Sibillini thrust sheet allowed us to fully evaluate the variability of the different attributes of the mesoscopic fracture patterns in relation with the geometry of the hosting fold, and to propose a constrained stress history. This had the twofold purpose of (1) providing a robust test for the different hypotheses on the relationships between extensional deformation and thrust-related folding at the mountain front of the northern Apennines, and (2) demonstrating that, even in the worst situation of three distinct but roughly coaxial deformation stages, integration of detailed field observations and simple geometrical analyses performed on a large mesostructural data set, allowed the stress evolution to be fully constrained.

2. Geological Outline [6] The study area is located in the southern portion of the Sibillini thrust sheet, in the Umbria-Marche region (Figures 1 and 2). The thrust sheet is characterized by the presence of two major extensional fault systems striking parallel to the frontal anticline (Figure 1b): the Quaternary Monte Vettore Fault (VF in Figure 1b) [Cello et al., 1997] to the south, and the Mt. San Vicino Fault to the north (SFV in Figure 1b), which is interpreted by different authors either as a mostly pre- [e.g., Mazzoli et al., 2002] or post-folding fault system [e.g., Boncio and Lavecchia, 2000]. The difference in elevation between the crest and the adjacent synclines ranges from 400 to 500 m up to 1000 m. The uplift of the hangingwall is greater than about 4 km (Figures 1e and 2c). This approximate value is constrained by reflection seismic profiles located few km to the north of the study area [Scarselli et al., 2007] and it has to be regarded as a first order value, as there are no direct information allowing to fully define the detailed deep geometry of the Sibillini thrust sheet in the study area. The Sibillini structure formed in Messinian to Pliocene time [Scarselli et al., 2007], with a first Messinian to early Pliocene stage followed by an out-of sequence middle Pliocene reactivation [Ghisetti and Vezzani, 1997]. The Sibillini thrust involves the Hercynian basement, as recognized in crustal-scale seismic sections [Barchi et al., 1998], and the overlying Permo-Triassic to Miocene sedimentary pile, which mostly includes limestones, marls and, in the upper portion, syn-tectonic siliciclastic sediments (Figure 2b). In the study area the frontal anticline strikes NNW–SSE and its hinge line has a negligible plunge than never exceeds 4 . In detail, the hinge line strikes about N163 in the northern portion of the study area, while to the south it strikes about N153 (Figure 2a). Average strike is about N160 , which is computed by

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Figure 2. (a) Geological map of the study area with location of field sites (black circles correspond to sites where S-C structures have been measured) and traces of cross section and structural transect. (b) Synthetic stratigraphic sequence. (c) Schematic cross section in the southern part of the study area. (d) Geological section across the thrust zone and the reactivated Jurassic extensional fault (modified and adapted from Lavecchia [1979]). (e) Detail of S-C structures in the thrust zone (Lat: 43 03.5′N; Long: 13 14′E). (f) Cumulative contouring, with data number and contouring interval, of poles to S and C structures and associated slickenlines collected along the Sibillini thrust. (g) Cumulative contouring of poles to bedding. Directions parallel and perpendicular to the fold hinge (F.H.) line are shown in these and in the following stereoplots. weighting the local strike of the hinge line along its trace in the study area. Two roughly N–S striking and westward dipping extensional fault zones are present in the southern portion of the study area, which partially reworked inherited

early Jurassic ones, as testified by thickness variation of Jurassic sediments across them (Figure 2d). The anticline is characterized by a constantly dipping backlimb (layers dip is about 30 ) and a smoothed transition to a flat-lying crestal

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Figure 3. Cumulative contouring of poles to pressure solution cleavages (a) in their present orientation and (b) after bedding dip removal (bedding is removed by using the method of Ramsay [1967]. (c) Pressure solution cleavages with detail of stylolitic teeth in the backlimb of the anticline, Scaglia Formation (Lat: 43 03.5′N; Long:13 10.5′E). sector. The forelimb has variable dip and includes an overturned sector (Figure 2d). In its southern portion, the anticline overrode another structure, possibly belonging to a system of east-verging thrusts splaying off from the Sibillini main ramp (Figure 2c). There the main thrust (which represents the trailing fault of the system responsible for uplift of the mountain front) is exposed [e.g., Lavecchia, 1985; Calamita, 1991; Leoni et al., 2007] (Figures 2c and 2d) and consists of a thick (up to 200 m) shear zone that largely incorporates the overturned forelimb panel [e.g., Lavecchia, 1979, 1985] (Figure 2d). Kinematic data from S-C structures (Figure 2e) collected along the thrust zone are clustered along a NE-SW orientation (Figure 2f), forming an angle of about 75 with the fold hinge line (Figure 2g). This indicates that the shortening direction was not perpendicular to the fold trend.

3. Structural Data [7] Data about pressure solution cleavages, joints, veins, and faults were collected in the central portion of the exposed multilayer (Figure 2a), which includes well bedded limestones, marly limestones and marls (form Corniola to Bisciaro formations; Figure 2b). [8] Mesofolds trending parallel to the host anticline have been also observed, particularly in the forelimb, where they concur to produce an apparent thickening of the upper portion of the multilayer (Scaglia + Marne a Fucoidi Fms.) of about 100 m (i.e., from about 400 to about 500 m). 3.1. Pressure Solution Cleavages [9] Pressure solution cleavages lie at high angle to bedding (Figure 3) and strike slightly oblique to the fold hinge line (Figures 3a and 3b), with the exception of few tectonic

cleavages at low angle to bedding, located in the crest and, particularly, in the forelimb. In this anticline the cleavage spacing (S) scales with layer thickness (H) and the scaling relationships between S and H in the two units where almost the entire cleavage data set has been collected (i.e., the Scaglia and Maiolica formations) are very similar [Tavani et al., 2010]. This cleavage set at high angle to bedding mostly occurs in the fold limbs and its frequency (computed as the ratio between host layer thickness and cleavage spacing, H/S [Tavani et al., 2006]) progressively reduces from the fold limbs toward the crest. This is shown by analyzing the variability of the cleavage H/S versus both bedding dip (Figure 4a) and across strike position (Figure 4b). Comparison between the H/S trend in the Scaglia and Maiolica formations, and the cumulative data set, show no relevant lithological bias. This supports the cumulative analysis of cleavage data. Sites in the crestal sector of the Sibillini frontal anticline are frequently uncleaved and where cleavage occurs its frequency is lower than in the limbs. A strong correlation exists between cleavage and bedding dip (Figure 4c) and when the latter is restored to the horizontal, the cleavage dip shows significant deviations from the vertical, with opposite dip directions in the two limbs (Figure 4d). The cleavage strike in the backlimb and in the steeper part of the forelimb forms a clockwise angle of about 20 with the fold axial strike. Such an angle reduces toward the poorly cleaved crest, to become negligible (even opposite) in the crest-forelimb transition (Figure 4e). Along the anticlinal hinge, the average cleavage strike is perpendicular to the transport direction provided by S-C arrays and constantly forms an angle of about 15 with the anticline hinge line, regardless of the local strike of the latter (Figure 4f). Cleavage frequency along the strike of the anticline slightly increases southward (Figure 4g).

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Figure 5. Cumulative contouring of poles to joints (a) in their present orientation and (b) after bedding dip removal. (c) Longitudinal joints in the crestal sector, Maiolica Formation and (d) detail of a longitudinal joint in the Maiolica Formation, showing plumose structure and fringe cracks (Lat: 43 04′N; Long:13 12.5′E). 3.2. Joints and Veins [10] Joints are clustered in two broad sets striking NNWSSE (longitudinal) and NE-SW (transversal), respectively (Figures 5a and 5b). The first set strikes parallel to the fold hinge line and includes both stratabound and non-stratabound elements (Figure 5c). The second joint set is oriented perpendicular to both cleavage and bedding, and is the less pervasive one . Longitudinal joints consist of polished surfaces with diagnostic features, like plumose structures and fringe cracks (Figure 5d), allowing to infer a non fluid assisted development and to discard any possible previous calcite infilling. Longitudinal joints are pervasive and closely spaced in the anticlinal crest, while they are rarely found in the fold limbs. Accordingly, robust joint spacing values are available only in the crestal sector and in the crest-limb transitional areas, while azimuth and dip values are available also in the fold limbs. Longitudinal joints are characterized by negligible variations of spacing at different bedding dip values (Figure 6a). On the contrary, their dip varies with varying the bedding dip, both in the present orientation and after bedding dip removal (Figures 6b and 6c). Longitudinal joints azimuth (Figure 6d) and spacing (Figure 6e) vary along the fold strike. Moving southward, spacing decreases and, as an average, the azimuth undergoes a progressive counterclockwise rotation, roughly following that of the fold hinge

line. Although longitudinal joints are found in the entire multilayer exposed in the crestal sector, they are particularly abundant in the Maiolica Formation. [11] Veins are less abundant than joints and their alongstrike length commonly does not exceed 20–30 cm. Their aperture is variable and mostly lower than 2–3 mm. Veins are clustered in three maxima at high angle to bedding (Figures 7a and 7b): the major one strikes NE-SW and the other two strike ENE-WSW and roughly N-S, respectively. Veins orientation was complemented with direct observations about both opening direction, where available (Figures 7c and 7d) and with the structural assemblage (Figures 7e and 7f). No evidence of oblique opening has been found in the ENE-WSW and N-S striking veins, while NE-SW striking ones are characterized by both wall-perpendicular and wall-oblique opening. 3.3. Faults [12] Faults are abundant and their length ranges from few cm to hundreds of meters. Most of them strike parallel to the anticlinal hinge line (Figures 8a and 8b) and the kinematics of the larger ones (excluding the main thrust fault) is mostly extensional. The rotaxes (or rotational axes), i.e., the direction on the fault plane perpendicular to slickenlines [e.g., Wise and Vincent, 1965; Salvini and Vittori, 1982;

Figure 4. Cross-sectional and along-strike data density contours. (a) Pressure solution cleavage H/S versus bedding dip. (b) Pressure solution cleavage H/S versus position along the transect in Figure 2a. (c) Pressure solution cleavage dip versus bedding dip. (d) Pressure solution cleavage dip after bedding dip removal, versus bedding dip. (e) Pressure solution cleavage azimuth versus bedding dip. (f) Pressure solution cleavage azimuth versus latitude. (g) Pressure solution cleavage H/S versus latitude. In this figure and in the following ones the frequency is computed on a 60 60 regular grid and data are normalized to 100 for each X interval. All the graphs include the entire cleavage data set with the exception of Figure 4b, which includes only data with a distance from the transect lower than 3 km; the along-transect position of each datum is that of its projection on the transect trace. 7 of 17

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Figure 6. Data density contours of (a) longitudinal joint spacing versus bedding dip (y axis has a logarithmic scale); (b) longitudinal joint dip versus bedding dip; (c) longitudinal joint dip after bedding dip removal versus bedding dip; (d) longitudinal joint azimuth versus latitude; (e) longitudinal joint spacing versus latitude (y axis has a logarithmic scale). Notice that the bedding dip intervals of Figures 6b and 6c are greater than that in Figure 6a. This is due to the fact that longitudinal joints in the fold limbs mostly occur as isolated surfaces, with no associated spacing value. Tavani et al., 2011], of normal and reverse faults, in both their present orientation and after removing the bedding dip, are clustered along a NNW-SSE direction (Figures 8c to 8f). Although the low data number does not permit a rigorous spatial analysis, the general observation is that contractional faults are mostly located in the limbs and close to the frontal thrust, while extensional faults are mainly located in the crest. Strike-slip faults commonly occur as small-scale conjugate arrays at high angle to bedding and include left-lateral and rightlateral faults striking roughly E-W and NE-SW, respectively

(sets A and B of Figures 8g and 8h). Strike-slip faults striking parallel to the hinge line of the host anticline also occur. The acute bisectors of the conjugate strike-slip fault sets are parallel and perpendicular to transversal joints and veins and to pressure solution cleavages, respectively. 3.4. Mesostructures Relative Chronology [13] Pressure solution cleavages, transversal joints and conjugate strike slip faults are roughly coeval, as documented by the presence of mutual crosscutting relationships

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Figure 7. Cumulative contouring of poles to vein (a) in their present orientation and (b) after bedding dip removal, with poles of veins having wall-perpendicular opening. (c) Photograph and (d) line-drawing of a bedding surface in the Maiolica Formation, showing an obliquely opening ENE-WSW-striking vein. The oblique displacement is marked by displaced NW-SE striking pressure solution cleavage and NE-SW striking vein. (e) Photograph and (f) line-drawing of a bedding surface in the Maiolica Formation. Longitudinal pressure solution cleavages are perpendicular to transversal veins and mutual crosscutting relationships between these elements exist, indicating their coeval development. Roughly N-S and E-W striking veins are also coeval with pressure solution cleavages and transversal veins. The presence of en echelon patterns indicates that these two sets correspond to right-lateral (N-S) and left-lateral (E-W) faults, as shown in the inset of the figure, although these faults do not display mesoscopic evidences of shear. Location of both photos is Lat: 43 03.5′N; Long:13 11′E.

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are also observed (Figures 10a–10f), together with longitudinal extensional faulting postdating both pressure solution cleavages (Figure 10i) and longitudinal joints (Figure 10j). In particular, we observed that longitudinal veins are particularly abundant close to post-contractional faults, where also small implosion breccias postdating pressure solution cleavages (Figures 10a, 10b, and 10f) and post-kinematic calcite filling previously developed joints (Figures 10g and 10h) are observed. Relationships between joints and pressure solution cleavages are only rarely observed and in these few cases joints postdate cleavages (Figures 10a, 10b, and 10d). Extensional faults with lengths greater than few meters frequently grow by linkage of previously developed joint arrays (Figures 11a–11c), which are not localized within damage zones but pervasively affect the entire crestal sector of the anticline. Moreover, rotated blocks associated with extensional faulting host joints that are rotated together with beds (Figure 10j). These observations indicate that major extensional faults developed after folding and widespread jointing (Figures 11d and 11e). [14] Non univocal crosscutting relationships between longitudinal pressure solution cleavages, joint, veins, and faults testify for the presence of two main coaxial extensional deformation events, separated by a contractional one.

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Figure 8. Fault data analysis. (a, b) Poles to fault and (c–f) rotaxes of normal (Figures 8c and 8d) and reverse (Figures 8e and 8f) faults. Slikenlines of (g) left-lateral and (h) right-lateral faults, after bedding dip removal. Average strike of the anticlinal hinge line and the direction perpendicular to it are shown. See text for details. (Figures 7e and 7f), which are observed also in other neighboring structures [e.g., Tavani et al., 2008]. Longitudinal contractional structures reworking inherited extensional ones are found (Figure 9), but opposite relationships

4.1. Structural Summary [15] Pressure solution cleavages, transversal joints and veins, and conjugate strike-slip faults are near perpendicular to bedding and define a compressional deformation pattern associated with a dynamic stress field having s2 near perpendicular to bedding and s1 striking parallel to the tectonic transport direction provided by S-C structures, and nonperpendicular to the fold hinge line (Figure 12). This deformation pattern can be interpreted as related with a layer parallel shortening (LPS) event, analogously to what described in many thrust-related anticlines [e.g., Gray and Mitra, 1993; Railsback and Andrews, 1995; Tavarnelli, 1997; Tavani et al., 2006]. It is worth noting that deformation structures developed during NE-SW oriented LPS have been largely documented in the northern Apennines [Marshak et al., 1982; Lavecchia et al., 1983; Barchi et al., 1991; Tavani et al., 2008]. However, these elements have been mostly measured in areas where the strike of the hosting anticlines is about NW-SE (i.e., perpendicular to the regional shortening direction), which did not allowed to discriminate between fold-perpendicular and tectonic transport-parallel LPS. In the studied anticline the overall amount of compressional strain reduces toward the crestal sector, as testified by the progressive decreases of cleavage frequency. The axis-symmetrical deviations from the vertical of the angle between cleavages and bedding surfaces indicate a small layer-parallel shear component [e.g., Tavani et al., 2004], which is oriented toward the fold hinge zone, consistently with flexural slip folding [Donath and Parker, 1964]. Accordingly, LPS occurred during thrust propagation and early folding [e.g., Tavani et al., 2006]. The few reverse faults observed in the area can be also included in this LPS assemblage. This, under the assumption that the different stress configuration inferred from these faults (i.e., a near vertical s3 instead of a near vertical s2 if an Andersonian

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Figure 9. Contractional longitudinal structures postdating extensional ones. (a) Photo and (b) line drawing of a positively inverted (and then rotated) extensional fault. The inversion is testified by the variation of layer displacement at different distances along the fault and by the presence of a buttress fold; forelimb, Scaglia Formation (Lat: 43 08.5′N; Long:13 11.5′E). (c) Photo and (d) line drawing of longitudinal pressure solution cleavages and veins at high angle to bedding in the backlimb (Maiolica Formation; Lat: 43 03.5′N; Long:13 10.5′E). Pressure solution cleavages are near perpendicular to bedding, with few exceptions represented by surfaces having a cut-off angle with bedding of about 60–70 . (e) Photo and (f) line drawing of one of these oblique to bedding cleavages showing stylolitic teeth being parallel to the bedding surface and oblique to the cleavage envelope surface. The cleavage postdates bedding perpendicular veins, and when (g) the teeth-parallel displacement associated with dissolution is removed, (h) the resulting geometry of these veins indicates that pressure solution cleavage has reworked an inherited extensional fault. model is assumed) is associable with local variabilities of the stress field. [16] The illustrated relationships between longitudinal extensional faults and bedding attitude indicate pre- and late to post-folding extensional deformations. In fact, most reverse faults in the present-day setting attain an extensional kinematics when bedding in the Cretaceous-Paleocene rocks is restored to the horizontal. This suggests pre-thrusting extension in the foredeep-foreland system induced by flexural bending [e.g., Calamita and Deiana, 1980; Mazzoli, 1994; Scisciani et al., 2001; Mazzoli et al., 2002], which is further supported by the observed contractional reactivation of extensional faults (Figure 9). Coherently with data from exposed foreland sectors [e.g., Billi and Salvini, 2003; Quintà and Tavani, 2012], our observations indicate that extensional deformation developed due to outer arc extension in the peripheral bulge of an orogenic system typically produces extensional structures having displacements lower

than few hundreds of meters. Closely spaced longitudinal joints have dip values varying with the bedding dip, both in the present orientation and after bedding dip removal. This indicates that longitudinal joints formed when bedding attitude was no longer horizontal and were further tilted during the final stages of fold amplification. The evidence that, with the exception of few deformation structures located near fault zones, pervasive longitudinal joints are mostly not filled by calcite and, consequently, they did not form in a fluid assisted environment, provides further indirect support to a late-stage extensional event. The mutual crosscutting relationships between longitudinal veins and pressure solution cleavages, and the paucity of observations about crosscutting relationship between pressure solution cleavages and longitudinal joints also support a late-stage extensional event. These observations, in fact, can be explained as follows: (1) small angular difference between joints and the cohesionless nature of pressure solution cleavages may have

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Figure 10. (a) Photo and (b) line drawing of a longitudinal extensional system postdating longitudinal pressure solution cleavages in the crestal sector, Scaglia Formation (Lat: 43 10.5′N; Long:13 10′E). (c, e) Pressure solution cleavages have well-developed stylolitic teeth and they are filled by insoluble material. (d) Cleavage in the left side of the photo in its lower portion propagates downward as a straight and sharp longitudinal joint. The anastomosed shape of the pressure solution segment indicates that it did not resulted from the reactivation of a joint but, instead, is the joint that nucleated from the lower tip of the pressure solution cleavage, and thus postdates the cleavage. (f) Cleavage in the right side of the photo is postdated by a small implosion breccia. Bedding parallel thin section, collected in the same outcrop of Figure 10a, observed under (g) normal and (h) polarized light, and showing post-kinematic calcite within transversal and longitudinal joints. Longitudinal extensional faults in the subhorizontal crest, with layer (i) in the drag of the footwall and (j) in the fault core hosting pressure solution cleavage and joints, respectively (shown in the insets) oriented perpendicular to bedding and rotated together with the layer during faulting. favored the slight reopening of cleavages rather than the development of new joints; (2) late-stage extensional deformation was mostly non-fluid assisted, with rare local exceptions mostly located in the vicinity of quaternary faults, where veins developed postdating and/or reopening

both pressure solution cleavages (Figures 10a, 10b, and 10f) and joints (Figures 10g and 10h). [17] The following scenario is consistent with all the discussed observations (Figure 13). The first deformation event caused by growth of the Apenninic thrust wedge was

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Figure 11. (a) Photo, (b) line drawing and (c) detail of an embryonic longitudinal extensional fault growing by linkage of near vertical joints, as testified by the presence of near vertical steps along the fault; Maiolica Formation in the crestal sector (Lat: 43 13.5′N; Long:13 07.’E). (d) Extensional faults in the crest-forelimb transition, Calcare Massiccio Fm (Lat: 43 04.5′N; Long:13 12.5′E). The main fault is a reactivated Jurassic element. The antithetic faults form small cutoff angles with bedding, suggesting a post-tilting development. (e) Frontal view of a N-S striking and westward dipping fault surface in the forelimb (Scaglia Fm.), showing slickenlines associated with both reverse (detail on the right) and normal (detail on the left) movements. longitudinal extensional faulting and veining, in a fluid assisted framework, induced by outer arc extension in the peripheral bulge of the orogenic system. The area was then incorporated at the toe of the thrust-and-fold belt and contractional strain caused overprinting of the inherited extensional structures that were positively inverted. Layer-parallel contraction produced the growth of the frontal anticline and the development of pressure solution cleavages mostly in the fold limbs. Tectonic thickening in the forelimb supports fold amplification by fault-propagation folding [e.g., Erslev, 1991; Zehnder and Allmendinger, 2000], with folding occurring synchronously with reverse faulting. Finally, latethrusting caused uplift and exhumation of the fold, with widespread longitudinal jointing and extensional faulting, particularly in the anticlinal crest (Figure 13), which continued during the Quaternary. 4.2. Insights on Stress Evolution During Thrusting and Folding [18] The first-order non perpendicularity between the tectonic transport direction of the Sibillini thrust sheet and the strike of the frontal anticline in the study area, relates with the fact that the latter is located in the southern portion of the regionally arched frontal structure. In fact, the strike of

pressure solution cleavages coincides with that of the hinge line of the host anticlines in its central portion, and this suggests that s1 all along the growing anticline was oriented parallel to the regional shortening direction. The slight variations of cleavage angle to bedding, which we relate to a

Figure 12. Schematic diagram of the deformation pattern in the frontal anticline of the Sibillini thrust sheet. See text for details.

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Figure 13. Relationships between tectonics stages, fold evolution and dominant deformation in the study anticline. top-to-hinge layer-parallel shear component, are not accompanied by organized variations of the cleavages strike, which is the same in the backlimb and in the steeper portion of the forelimb, indicating that the layer-parallel shear component was parallel to the regional shortening direction too. Deviation of the cleavage strike from perpendicularity to the regional shortening direction to parallel the anticlinal hinge line occurs only in the crest-forelimb transition. Coherently with numerical models [e.g., Bellahsen et al., 2006b], this localized change of pressure solution cleavage orientation can be interpreted as the result of stress perturbation during upward thrust fault propagation and noncylindrical fold tightening. [19] The slight obliquity between pressure solution cleavage and hinge line of the hosting anticline provides a first-order information ruling out inner-arc compression in the leading and trailing synclines [e.g., Ramsay, 1967] as the cause of the contractional strain increment observed in the fold limbs. In this case, in fact, a perpendicularity between maximum curvature (i.e., the synclinal hinge line direction) and pressure solution cleavage average strike is expected. The bulk proportionality between cleavages frequency and magnitude of s1 [Alvarez et al., 1978] indicates an early

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syn-folding decrease of the latter toward the crest of the studied anticline, which was maintained also during the latefolding deformation stage, as indicated by the preferential location of pervasive longitudinal joints in the anticlinal crest. These tensile deformation structures are abundantly documented in thrust-related anticlines [e.g., Stearns, 1968; Price and Cosgrove, 1990; Srivastava and Engelder, 1990; Lemiszki et al., 1994], and are commonly interpreted as induced by outer-arc extension during either fixed-hinge [e.g., Lisle, 1994; Fischer and Wilkerson, 2000] or activehinge folding [Srivastava and Engelder, 1990], flexural-slip/ flow folding [e.g., Engelder and Peacock, 2001], or gravitational collapse [e.g., Morley, 2007]. The axis-symmetrical deviations from the vertical of the angle between longitudinal joints and bedding surfaces observed in the study structures, are opposite to what expected during flexural-folding, where joints should dip toward the hinge once the bedding dip is removed [e.g., Engelder and Peacock, 2001]. The presence of longitudinal joints in the zero-curvature crestal sector, which was not transported above an upper decollement, rules out syn-folding outer-arc extension as the deforming mechanism responsible for joint development. [20] Many features of the late-folding extensional pattern, including the evidence that longitudinal joints frequency increases in the southern, more uplifted, sectors, well-fit into a gravitational collapse scenario. Accordingly, pervasive longitudinal jointing in the crestal sector of the frontal anticline in the Sibillini thrust sheet is interpreted as the ultimate effect of the magnitude decrease of the horizontal stress in the anticlinal crest during late-stage thrusting. Erosional exhumation of the crestal sector, which was uplifted of more than 4 km, enhanced such a decrease and eventually resulted in a local stress field characterized by a vertical s1 and a s2 striking parallel to the direction corresponding to the minimum topographic slope, which offers the major resistance to lateral rock expansion induced by the vertical load. This direction is the fold hinge line and, as a consequence, s3 is oriented perpendicular to it. Accordingly, pervasive longitudinal joints in the study anticline can be regarded, at least partially, as unloading joints [e.g., Engelder, 1985], as previously hypothesized by Di Naccio et al. [2005]. This inference is consistent with the numerical results of Savage and Swolfs [1986], showing that in contractional settings the gravitational stress induced by a ridge produces the decrease of the horizontal component of the stress field and can cause the onset of extensional conditions in the ridge zone, i.e., in the growing anticline. It is reasonable to assume cross-sectional widening and downward propagation of the horizontal stress magnitude reduction area during late thrusting and fold exhumation. Eventually, involvement of the thrust ramp into the expanding extensional domain may cause its negative inversion as an extensional fault segment. This scenario supports the idea that an important amount of the extensional deformation observed at the mountain front of the Apennines is late-thrusting in time [e.g., Ghisetti and Vezzani, 2000; Patacca et al., 2008]. [21] From the analyzed data set an important final consideration on folding-related fracturing arises. The clear synfolding origin of pressure solution cleavages supports the existence of a strong stress channelization in well-layered sedimentary packages deforming by flexural-slip folding. In a cross-sectional approach, it has been previously proposed

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that when flexural slip occurs at very low friction along the bedding surface, s1 tends to remain almost parallel to bedding [e.g., Ohlmacher and Aydin, 1995; Tavani et al., 2006]. Callot et al. [2010] proposed that this mechanism of stress channelization operates up to few degree of bed tilting, depending on the frictional properties of bedding surfaces. In the studied formations of the Sibillini thrust sheet, beds are commonly separated by thin clay interlayers, indicating a very low friction between beds. Our results show that cleavage tends to remains almost perpendicular to bedding also at high bedding dip values. In particular, the deviation from the vertical is less than 10 for bedding dips lower than 30 , and exceeds 15 only for bedding dip values greater than 50–60 . The same process operates in map view and, in particular, in agreement with data from the few other oblique structures where mesostructural data have been collected [e.g., Tavani et al., 2011], data presented in this work indicate that the orientation of syn-folding deformation structures developed during layer-parallel shortening geometrically relates with the tectonic transport direction rather than with the fold geometry.

5. Conclusions [22] Structural data collected in the Umbria-Marche carbonate multilayer involved in the frontal anticline of the Sibillini thrust sheet indicate the presence of two syn orogenic extensional deformation event that have occurred before and, above all, in the later stages of folding and thrusting. Pre-folding extension in the foreland basin of the Apenninic thrust wedge undergoing flexural bending led to the development of longitudinal deformation structures that were postdated by syn-folding layer-parallel shortening. The pattern of these contractional deformation structures, particularly pressure solution cleavages, indicates that a decrease of the horizontal component of the stress field paralleling the regional shortening direction has occurred in the crestal sector of the frontal anticline since the early stages of folding. Such a decrease was enhanced by uplift and erosional exhumation of the anticline during the later stage of thrusting. This resulted in the development of pervasive longitudinal jointing and extensional faulting in the flatlying crestal sector, which cannot be ascribed to syn-folding outer arc extension but, instead, to syn-contractional latestage gravitational collapse. [23] Acknowledgments. Authors thank N. Bellahsen and two anonymous reviewers for their criticisms and suggestions, which greatly improved the paper . This work was carried out with the financial support of the MODES-4D (CGL2007-66431-C02-125 02/BTE) project, the Repsol YPF and the Italian MIUR.

References Agosta, F., and A. Aydin (2006), Architecture and deformation mechanism of a basin-bounding normal fault in Mesozoic platform carbonates, central Italy, J. Struct. Geol., 28, 1445–1467, doi:10.1016/j.jsg.2006.04.006. Alvarez, W. (1990), Pattern of extensional faulting in pelagic carbonates of the Umbria–Marche Apennines of central Italy, Geology, 18, 407–410, doi:10.1130/0091-7613(1990)0182.3.CO;2. Alvarez, W., T. Engelder, and P. Geiser (1978), Classification of solution cleavage in pelagic limestones, Geology, 6, 263–266, doi:10.1130/ 0091-7613(1978)62.0.CO;2. Antonellini, A., E. Tondi, F. Agosta, A. Aydin, and G. Cello (2008), Failure modes in deep-water carbonates and their impact for fault development: Majella Mountain, central Apennines, Italy, Mar. Pet. Geol., 25, 1074–1096, doi:10.1016/j.marpetgeo.2007.10.008.

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Barchi, M., G. Lavecchia, M. Menichetti, G. Minelli, G. Pialli, and S. Nardon (1991), Analisi della fratturazione del Calcare Massiccio in una struttura anticlinalica dell’Appennino umbro-marchigiano, Boll. Soc. Geol. Ital., 110, 101–124. Barchi, M., G. Minelli, and G. Pialli (1998), The CROP-03 profile: A synthesis of results on deep structures of the northern Apennines, Mem. Soc. Geol. Ital., 52, 383–400. Beaudoin, N., R. Leprêtre, N. Bellahsen, O. Lacombe, K. Amrouch, J.-P. Callot, L. Emmanuel, and J.-M. Daniel (2012), Structural and microstructural evolution of the Rattlesnake Mountain Anticline (Wyoming, USA): New insights into the Sevier and Laramide orogenic stress build-up in the Bighorn Basin, Tectonophysics, doi:10.1016/j.tecto.2012.03.036, in press. Bellahsen, N., P. Fiore, and D. D. Pollard (2006a), The role of fractures in the structural interpretation of Sheep Mountain Anticline, Wyoming, J. Struct. Geol., 28, 850–867, doi:10.1016/j.jsg.2006.01.013. Bellahsen, N., P. Fiore, and D. D. Pollard (2006b), From spatial variation of fracture patterns to fold kinematics: A geomechanical approach, Geophys. Res. Lett., 33, L02301, doi:10.1029/2005GL024189. Bergbauer, S., and D. D. Pollard (2004), A new conceptual fold–fracture model including prefolding joints, based on field data from the Emigrant Gap anticline, Wyoming, Geol. Soc. Am. Bull., 116, 294–307, doi:10.1130/B25225.1. Bigi, G., D. Cosentino, M. Parlotto, R. Sartori, and P. Scandone (1990), Structural model of Italy and gravity map, 1:500.000, vol. 3, issue 14, Quaderni Ric. Sci., CNR, Rome. Billi, A., and F. Salvini (2003), Development of systematic joints in response to flexure-related fibre stress in flexed foreland plates: The Apulian forebulge case history, Italy, J. Geodyn., 36, 523–536, doi:10.1016/ S0264-3707(03)00086-3. Boncio, P., and G. Lavecchia (2000), A structural model for active extension in central Italy, J. Geodyn., 29, 233–244, doi:10.1016/S0264-3707 (99)00050-2. Boncio, P., F. Brozzetti, and G. Lavecchia (2000), Architecture and seismotectonics of a regional low-angle normal fault zone in central Italy, Tectonics, 19, 1038–1055, doi:10.1029/2000TC900023. Calamita, F. (1991), Extensional mesostructures in thrust shear zones: Examples from the Umbro-Marchean Apennines, Boll. Soc. Geol. Ital., 110, 649–660. Calamita, F., and G. Deiana (1980), Evidenze di una fase tettonica distensiva del Messiniano basale nel bacino di Camerino (Appennino umbromarchigiano), Stud. Geol.Camerti, 7, 7–11. Calamita, F., A. Pizzi, M. Ridolfi, G. Rusciadelli, and V. Scisciani (1998), Il buttressing delle faglie sinsedimentarie pre-thrusting sulla strutturazione neogenica della catena: L’esempio della M.gna dei Fiori (Appennino centrale esterno), Boll. Soc. Geol. Ital, 118, 125–140. Calamita, F., M. Coltorti, D. Piccinini, P. P. Pierantoni, A. Pizzi, M. Ripepe, V. Scisciani, and E. Turco (2000), Quaternary faults and seismicity in the Umbro-Marchean Apennines (central Italy): Evidence from the 1997 Colfiorito earthquake, J. Geodyn., 29, 245–264, doi:10.1016/ S0264-3707(99)00054-X. Calamita, F., S. Satolli, V. Scisciani, P. Esestime, and P. Pace (2011), Contrasting styles of fault reactivation in curved orogenic belts; examples from the central Apennines (Italy), Geol. Soc. Am. Bull., 123, 1097–1111, doi:10.1130/B30276.1. Callot, J.-P., P. Robion, W. Sassi, M. L. E. Guiton, J.-L. Faure, J.-M. Daniel, J.-M. Mengus, and M. Schmitz (2010), Magnetic characterisation of folded aeolian sandstones: Interpretation of magnetic fabrics in diamagnetic rocks, Tectonophysics, 495, 230–245, doi:10.1016/j.tecto.2010. 09.020. Carminati, E., D. Scrocca, and C. Doglioni (2010), Compaction-induced stress variations with depth in an active anticline: northern Apennines, Italy, J. Geophys. Res., 115, B02401, doi:10.1029/2009JB006395. Castellarin, A., R. Colacicchi, and A. Praturion (1978), Fasi distensive, trascorrenze e sovrascorrimenti lungo la linea Ancona-Anzio dal Lias al Pliocene, Geol. Romana, 17, 161–189. Cavinato, G. P., and P. G. DeCelles (1999), Extensional basins in the tectonically bimodal central Apennines fold-thrust belt, Italy: Response to corner flow above a subducting slab in retrograde motion, Geology, 27, 955–958, doi:10.1130/0091-7613(1999)0272.3.CO;2. Cello, G., S. Mazzoli, E. Tondi, and E. Turco (1997), Active tectonics in the central Apennines and possible implications for seismic hazard analysis in peninsular Italy, Tectonophysics, 272, 43–68, doi:10.1016/S00401951(96)00275-2. Chiarabba, C., P. De Gori, and A. Amato (2011), Do earthquake storms repeat in the Apennines of Italy?, Terra Nova, 23, 300–306, doi:10.1111/j.1365-3121.2011.01013.x. Collettini, C., M. Barchi, C. Pauselli, C. Federico, and G. Pialli (2000), Seismic expression of active extensional faults in northern Umbria

15 of 17

TC4019


(central Italy), J. Geodyn., 29, 309–321, doi:10.1016/S0264-3707(99) 00059-9. D’Agostino, N., N. Chamot-Rooke, R. Funiciello, L. Jolivet, and F. Speranza (1998), The role of pre-existing thrust faults and topography on the styles of extension in the Gran Sasso range (central Italy), Tectonophysics, 292, 229–254, doi:10.1016/S0040-1951(98)00070-5. D’Agostino, N., S. Mantenuto, E. D’Anastasio, A. Avallone, M. Barchi, C. Collettini, F. Radicioni, A. Stoppini, and G. Fastellini (2009), Contemporary crustal extension in the Umbria–Marche Apennines from regional CGPS networks and comparison between geodetic and seismic deformation, Tectonophysics, 476, 3–12, doi:10.1016/j.tecto.2008.09.033. De Paola, N., F. Mirabella, M. Barchi, and F. Burchielli (2006), Early orogenic normal faults and their reactivation during thrust belt evolution: The Gubbio Fault case study, Umbria-Marche Apennines (Italy), J. Struct. Geol., 28, 1948–1957, doi:10.1016/j.jsg.2006.06.002. Di Naccio, D., P. Boncio, S. Cirilli, F. Casaglia, E. Morettini, G. Lavecchia, and F. Brozzetti (2005), Role of mechanical stratigraphy on fracture development in carbonate reservoirs: Insights from outcropping shallow water carbonates in the Umbria-Marche Apennines, Italy, J. Volcanol. Geotherm. Res., 148, 98–115, doi:10.1016/j.jvolgeores.2005.03.016. Donath, F. A., and R. B. Parker (1964), Folds and folding, Geol. Soc. Am. Bull., 75, 45–62, doi:10.1130/0016-7606(1964)75[45:FAF]2.0.CO;2. Elter, P., G. Giglia, M. Tongiorgi, and L. Trevisan (1975), Tensional and compressional areas in the recent (Tortonian to present) evolution of north Apennines, Boll.Geofis. Teor. Appl., 17, 3–18. Engelder, T. (1985), Loading paths to joint propagation during a tectonic cycle: An example from the Appalachian Plateau, U.S.A, J. Struct. Geol., 7, 459–476, doi:10.1016/0191-8141(85)90049-5. Engelder, T., and D. C. P. Peacock (2001), Joint development normal to regional compression during flexural-flow folding: The Lilstock buttress anticline, Somerset, England, J. Struct. Geol., 23, 259–277, doi:10.1016/ S0191-8141(00)00095-X. Erslev, E. A. (1991), Trishear fault-propagation folding, Geology, 19, 617–620, doi:10.1130/0091-7613(1991)0192.3.CO;2. Evans, M. A. (2010), Temporal and spatial changes in deformation conditions during the formation of the central Appalachian fold-and-thrust belt: Evidence from joints, vein mineral paragenesis, and fluid inclusions, in From Rodinia to Pangea: The Lithotectonic Record of the Appalachian Region, edited by R. Tollo et al., Mem. Geol. Soc. Am., 206, 477–552, doi:10.1130/2010.1206(21). Fischer, M. P., and M. S. Wilkerson (2000), Predicting the orientation of joints from fold shape: Results of pseudo-three-dimensional modeling and curvature analysis, Geology, 28, 15–18, doi:10.1130/0091-7613 (2000)282.0.CO;2. Fubelli, G., S. Gori, E. Falcucci, F. Galadini, and P. Messina (2009), Geomorphic signatures of recent normal fault activity versus geological evidence of inactivity: Case studies from the central Apennines (Italy), Tectonophysics, 476, 252–268, doi:10.1016/j.tecto.2008.10.026. Geiser, P. A. (1988), Mechanisms of thrust propagation: Some examples and implications for the analysis of overthrust terranes, J. Struct. Geol., 10, 829–845, doi:10.1016/0191-8141(88)90098-3. Ghisetti, F., and L. Vezzani (1997), Interfering paths of deformation and development of arcs in the fold-and-thrust belt of the central Apennines (Italy), Tectonics, 16, 523–536, doi:10.1029/97TC00117. Ghisetti, F., and L. Vezzani (2000), Detachments and normal faulting in the Marche fold-and-thrust belt (central Apennines, Italy): Inferences on fluid migration paths, J. Geodyn., 29, 345–369, doi:10.1016/S0264-3707(99) 00057-5. Ghisetti, F., and L. Vezzani (2002), Normal faulting, extension and uplift in the outer thrust belt of the central Apennines (Italy): Role of the Caramanico fault, Basin Res., 14, 225–236, doi:10.1046/j.1365-2117. 2002.00171.x. Graham, B., M. Antonellini, and A. Aydin (2003), Formation and growth of normal faults in carbonates within a compressive environment, Geology, 31, 11–14, doi:10.1130/0091-7613(2003)0312.0.CO;2. Gray, M. B., and G. Mitra (1993), Migration of deformation fronts during progressive deformation: Evidence from detailed structural studies in the Pennsylvania Anthracite region, U.S.A, J. Struct. Geol., 15, 435–449, doi:10.1016/0191-8141(93)90139-2. Jolivet, L., et al. (1998), Midcrustal shear zones in postorogenic extension: Example from the northern Tyrrhenian Sea, J. Geophys. Res., 103, 12,123–12,160, doi:10.1029/97JB03616. Lacombe, O., N. Bellahsen, and F. Mouthereau (2011), Fracture patterns in the Zagros Simply Folded Belt (Fars): New constraints on early collisional tectonic history and role of basement faults, Geol. Mag., 148, 940–963, doi:10.1017/S001675681100029X. Lavecchia, G. (1979), Analisi cinematica del sovrascorrimento del Fiastrone (M.ti Sibillini nord-orientali), Boll. Soc. Geol. Ital, 98, 457–468.

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Lavecchia, G. (1985), Il sovrascorrimento dei Monti Sibillini: Analisi strutturale e cinematica, Boll. Soc. Geol. Ital, 104, 161–194. Lavecchia, G., G. Minelli, and G. Pialli (1983), Strutture plicative minori dell’ Appennino umbro-marchigiano, Boll. Soc. Geol. Ital, 102, 95–112. Lavecchia, G., F. Brozzetti, M. Barchi, M. Menichetti, and J. V. A. Keller (1994), Seismotectonic zoning in east-central Italy deduced from an analysis of the Neogene to present deformations and related stress fields, Geol. Soc. Am. Bull., 106, 1107–1120, doi:10.1130/0016-7606(1994) 1062.3.CO;2. Lemiszki, P. J., J. D. Landes, and R. D. Hatcher Jr. (1994), Controls on hinge-parallel extension fracturing in single-layer tangential-longitudinal strain folds, J. Geophys. Res., 99, 22,027–22,041, doi:10.1029/ 94JB01853. Leoni, L., P. Vannucchi, G. Principi, and F. Catani (2007), Deformation pattern in the underthrust carbonate-rich sequence of the Sibillini Thrust (central Italy): Insights for shear zone evolution in modern subduction complexes, Geodin. Acta, 20, 53–69, doi:10.3166/ga.20.53-69. Lisle, R. J. (1994), Detection of zones of abnormal strains in structures using Gaussian curvature analysis, AAPG Bull., 78, 1811–1819. Marchegiani, L., G. Bertotti, G. Cello, G. Deiana, S. Mazzoli, and E. Tondi (1999), Pre-orogenic tectonics in the Umbria-Marche sector of the AfroAdriatic continental margin, Tectonophysics, 315, 123–143, doi:10.1016/ S0040-1951(99)00277-2. Marshak, S., and T. Engelder (1985), Development of cleavage in limestones of a fold-thrust belt in eastern New York, J. Struct. Geol., 7, 345–359, doi:10.1016/0191-8141(85)90040-9. Marshak, S., P. A. Geiser, W. Alvarez, and T. Engelder (1982), Mesoscopic fault array of the northern Umbrian Apennine fold belt, Italy: Geometry of conjugate shear by pressure-solution slip, Geol. Soc. Am. Bull., 93, 1013–1022, doi:10.1130/0016-7606(1982)932.0.CO;2. Mattei, M. (1987), Analisi geologico-strutturale della Montagna dei Fiori (Ascoli Piceno, Italia centrale), Geol. Romana, 26, 327–347. Mazzoli, S. (1994), Early deformation features in synorogenic Messinian sediments of the northern Marchean Apennines (Italy), Ann. Tect., 8, 134–147. Mazzoli, S., G. Deiana, S. Galdenzi, and G. Cello (2002), Miocene faultcontrolled sedimentation and thrust propagation in the previously faulted external zones of the Umbria–Marche Apennines, Italy, EGU Stephan Mueller Spec. Publ. Ser., 1, 195–209, doi:10.5194/smsps-1-195-2002. Migliorini, C. I. (1948), I cunei composti nell’orogenesi, Boll. Soc. Geol. Ital, 67, 29–142. Morley, C. K. (2007), Development of crestal normal faults associated with deepwater fold growth, J. Struct. Geol., 29, 1148–1163, doi:10.1016/j. jsg.2007.03.016. Ohlmacher, G. C., and A. Aydin (1995), Progressive deformation and fracture patterns during foreland thrusting in the southern Appalachians, Am. J. Sci., 295, 943–987, doi:10.2475/ajs.295.8.943. Patacca, E., R. Sartori, and P. Scandone (1990), Tyrrhenian basin and Apenninic arcs: Kinematic relations since Late Tortonian times, Mem. Soc. Geol. Ital., 45, 425–451. Patacca, E., P. Scandone, E. Di Luzio, G. P. Cavinato, and M. Parotto (2008), Structural architecture of the central Apennines: Interpretation of the CROP 11 seismic profile from the Adriatic coast to the orographic divide, Tectonics, 27, TC3006, doi:10.1029/2005TC001917. Price, N. J., and J. W. Cosgrove (1990), Analysis of Geological Structures, Cambridge Univ. Press, Cambridge, U. K. Quintà, A., and S. Tavani (2012), The foreland deformation in the southwestern Basque-Cantabrian Belt (Spain), Tectonophysics, doi:10.1016/ j.tecto.2012.02.015, in press. Railsback, L. B., and L. M. Andrews (1995), Tectonic stylolites in the “undeformed” Cumberland Plateau of southern Tennessee, J. Struct. Geol., 17, 911–915, doi:10.1016/0191-8141(94)00127-L. Ramsay, J. G. (1967), Folding and Fracturing of Rocks, McGraw-Hill, New York. Salvini, F., and E. Vittori (1982), Analisi strutturale della linea Olevano Antrodoco Posta (Ancona-Anzio Auct.): Metodologia di studio delle deformazioni fragili e presentazione del tratto meridionale, Mem. Soc. Geol. Ital., 24, 337–355. Santantonio, M. (1993), Facies associations and evolution of pelagic carbonate platform/basin systems. Examples from the Italian Jurassic, Sedimentology, 40, 1039–1067, doi:10.1111/j.1365-3091.1993.tb01379.x. Savage, W. Z., and H. S. Swolfs (1986), Tectonic and gravitational stress in long symmetric ridges and valleys, J. Geophys. Res., 91, 3677–3685, doi:10.1029/JB091iB03p03677. Scarselli, S., G. D. H. Simpson, A. Allen, G. Minelli, and L. Gaudenzi (2007), Association between Messinian drainage network formation and major tectonic activity in the Marche Apennines (Italy), Terra Nova, 19, 74–81, doi:10.1111/j.1365-3121.2006.00717.x.

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Scisciani, V., F. Calamita, E. Tavarnelli, G. Rusciadelli, G. Ori, and W. Paltrinieri (2001), Foreland-dipping normal faults in the inner ridge of syn-orogenic basins: A case from the central Apennines, Italy, Tectonophysics, 330, 211–224, doi:10.1016/S0040-1951(00)00229-8. Silliphant, L. J., T. Engelder, and M. R. Gross (2002), The state of stress in the limb of the Split Mountain anticline, Utah: Constraints placed by transacted joints, J. Struct. Geol., 24, 155–172, doi:10.1016/S01918141(01)00055-4. Srivastava, D. C., and T. Engelder (1990), Crack-propagation sequence and pore-fluid conditions during fault-bend folding in the Appalachian Valley and Ridge, central Pennsylvania, Geol. Soc. Am. Bull., 102, 116–128, doi:10.1130/0016-7606(1990)1022.3.CO;2. Stearns, D. W. (1968), Certain aspect of fracture in naturally deformed rocks, in Rock Mechanics Seminar, edited by R. E. Riecker, pp. 97–118, Terr. Sci. Lab, Bedford, Mass. Storti, F. (1995), Tectonics of the Punta Bianca promontory: Insights for the evolution of the northern Apennines-northern Tyrrhenian Sea basin, Tectonics, 14, 832–847, doi:10.1029/95TC01203. Storti, F., and F. Salvini (2001), The evolution of a model trap in the central Apennines, Italy: Fracture patterns, fault reactivation and development of cataclastic rocks in carbonates at the Narni anticline, J. Pet. Geol., 24, 171–190, doi:10.1111/j.1747-5457.2001.tb00666.x. Tavani, S., L. Louis, C. Souque, P. Robion, F. Salvini, and D. Frizon de Lamotte (2004), Folding related fracture pattern and physical properties of rocks in the Chaudrons ramp-related anticline (Corbiéres, France), in Deformation, Fluid Flow and Reservoir Appraisal in Foreland Fold and Thrust Belts, edited by R. Swennen, F. Roure, and J. Granath, AAPG Mem., 1, 257–275. Tavani, S., F. Storti, O. Fernández, J. A. Muñoz, and F. Salvini (2006), 3-D deformation pattern analysis and evolution of the Añisclo anticline, southern Pyrenees, J. Struct. Geol., 28, 695–712, doi:10.1016/j.jsg. 2006.01.009. Tavani, S., F. Storti, F. Salvini, and C. Toscano (2008), Stratigraphic versus structural control on the deformation pattern associated with the evolution

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of the Mt. Catria anticline, Italy, J. Struct. Geol., 30, 664–681, doi:10.1016/j.jsg.2008.01.011. Tavani, S., F. Storti, and J. A. Munoz (2010), Scaling relationships between stratabound pressure solution cleavage spacing and layer thickness in a folded carbonate multilayer of the northern Apennines (Italy), J. Struct. Geol., 32, 278–287, doi:10.1016/j.jsg.2009.12.004. Tavani, S., J. Mencos, J. Bausà, and J. A. Muñoz (2011), The fracture pattern of the Sant Corneli Bóixols oblique inversion anticline (Spanish Pyrenees), J. Struct. Geol., 33, 1662–1680, doi:10.1016/j.jsg.2011.08.007. Tavarnelli, E. (1996), Ancient synsedimentary structural control on thrust ramp development: An example from the northern Apennines, Italy, Terra Nova, 8, 65–74, doi:10.1111/j.1365-3121.1996.tb00726.x. Tavarnelli, E. (1997), Structural evolution of a foreland fold-and-thrust belt: The Umbria-Marche Apennines, Italy, J. Struct. Geol., 19, 523–534, doi:10.1016/S0191-8141(96)00093-4. Tavarnelli, E., and D. C. P. Peacock (1999), From extension to contraction in syn-orogenic foredeep basins: The Contessa section, Umbria-Marche Apennines, Italy, Terra Nova, 11, 55–60, doi:10.1046/j.1365-3121.1999. 00225.x. Tondi, E., M. Antonellini, A. Aydin, L. Marchegiani, and G. Cello (2006), The role of deformation bands, stylolites and sheared stylolites in fault development in carbonate grainstones of Majella Mountain, Italy, J. Struct. Geol., 28, 376–391, doi:10.1016/j.jsg.2005.12.001. Vitale, S., F. Dati, S. Mazzoli, S. Ciarcia, V. Guerriero, and A. Iannace (2012), Modes and timing of fracture network development in poly deformed carbonate reservoir analogues, Mt. Chianello, southern Italy, J. Struct. Geol., 37, 223–235, doi:10.1016/j.jsg.2012.01.005. Wise, D. U., and R. J. Vincent (1965), Rotation axis method for detecting conjugate planes in calcite petrofabric, Am. J. Sci., 263, 289–301, doi:10.2475/ajs.263.4.289. Zehnder, A. T., and R. W. Allmendinger (2000), Velocity field for the trishear model, J. Struct. Geol., 22, 1009–1014, doi:10.1016/S01918141(00)00037-7.

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