Abstract
AbstractSeveral orogenic belts exhibit regional-scale anticlines characterized by prominent faults in their crestal/forelimb zone. These faults are also a common feature in the Neogene fold-and-thrust belt of the Apennines, where they have been contrastingly interpreted as younger-on-older thrust faults, large-scale strike-slip faults, and pre- or syn-thrusting normal faults. In this study, we analysed a NW–SE-trending fault (Montagna dei Fiori Fault) that affects the hinge-zone/forelimb of the Montagna dei Fiori Anticline. This fold is the outermost exposed contractional structure within the Pliocene–Quaternary antiformal stack of the outer Central Apennines. The integration of stratigraphic and structural data collected during a field geological survey enabled us to reconstruct a multiphase reactivation and deformation along the Montagna dei Fiori Fault. From the novel field data, a different interpretation for the evolution of the Montagna dei Fiori Fault is proposed. The fault originated as a Late Cretaceous – middle Miocene, NE-dipping, Dinaric up-thrust and was later reactivated, displaced and rotated during Pliocene Apennine thrusting and related folding, until assuming a present-day SW-dipping attitude with an apparent normal fault character. This newly proposed Dinaric origin of the Montagna dei Fiori structure is compared with an analogous subsurface example of a Palaeogene–Quaternary structure imaged by seismic reflection profile in the Adriatic foreland. The outcome of this combined field and subsurface investigation provides new elements to unravel the complex evolution of the Apennine thrust belt that developed at the expense of a previously deformed foreland, ahead of the advancing Dinaric chain.
Highlights
Regional hinterland-dipping faults realizing younger-on-older contacts in the hinge/forelimb zone of prominent thrust-related anticlines are commonly found in orogenic belts that have experienced both pre-orogenic and post-orogenic extensional events
Examples from the Central Apennine thrust belt of Italy have been contrastingly interpreted by different authors as (1) younger-on-older thrust faults within out-of-sequence thrust systems (Ghisetti & Vezzani, 1991; Carminati et al 2013); (2) regional strike-slip faults (Montone & Salvini 1991; Corrado et al 1998); (3) pre-thrusting normal faults (Tavarnelli, 1996; Calamita et al 1998, 2011, 2018; Scisciani et al 2001a; Mazzoli et al 2002; Pace et al 2014); (4) normal faults related to syn-thrusting activity (Migliorini, 1948; Ghisetti & Vezzani, 2000; Storti et al 2018); (5) back-thrusts related to Neogene Apennine thrusting (Patacca et al 2008; Fabbi & Smeraglia 2020); and (6) normal faults related to late-thrusting extensional collapse (Tavani et al 2012)
The tectonic significance of these faults has largely been debated in the literature with contrasting interpretations considering younger-on-older thrusts within out-of-sequence thrust systems (Ghisetti & Vezzani, 1991; Carminati et al 2014), regional strike-slip faults (Montone & Salvini 1991; Corrado et al 1998), pre-thrusting normal faults (Tavarnelli, 1996; Calamita et al 1998, 2011, 2018; Scisciani et al 2001b; Mazzoli et al 2002; De Paola et al 2006; Pace et al 2014) or normal faults related to syn-thrusting activity (Migliorini, 1948; Ghisetti & Vezzani, 2000; Storti et al 2018) and back-thrusts related to Neogene Apennine thrusting (Patacca et al 2008; Fabbi & Smeraglia 2020) or late-thrusting extensional collapse (Tavani et al 2012)
Summary
Regional hinterland-dipping faults realizing younger-on-older contacts in the hinge/forelimb zone of prominent thrust-related anticlines are commonly found in orogenic belts that have experienced both pre-orogenic and post-orogenic extensional events. Foreland domains ahead of contractional orogens are characterized by normal faulting related to lithospheric flexure during mountain building (Boccaletti et al 1990; Bradley & Kidd, 1991; Doglioni, 1995; Tavani et al 2015). These faults can be reactivated with reverse kinematics, displaced and/or rotated until reaching an overturned attitude during the progressive migration of orogenic contraction into the foreland (Butler, 2009; Calamita et al 2018). The newly proposed pre-Apennines model for the Montagna dei Fiori structure, involved in the frontal Pliocene– Quaternary antiformal stack of the Central Apennines, is compared with subsurface analogues that can be found among the Palaeogene–Quaternary structures of the Mid-Adriatic ridge in the Adriatic foreland (Fig. 2)
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