Late thrusting extensional collapse at the mountain front of the northern Apennines (Italy)

Abstract

[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.

Slab bending, syn‐subduction normal faulting, and out‐of‐sequence thrusting in the Central Apennines

“…The inferred displacements are consistent with those observed in present‐day foreland areas [e.g., Billi and Salvini , ; Quintà and Tavani , ; Tavani et al ., ]. The computed displacement rates range from 0.18 to 0.59 mm/a [ Fabbi , ].…”

“…It has also been proposed that extensional tectonics in the internal sectors of the Southern Apennines may be related with the adjustment of the wedge in order to lower its slope [ Casciello et al ., ; Mazzoli et al ., ]. Finally, it has been proposed that extensional faults also developed during the growth of thrust‐related folds [ Tavani et al ., ].…”

Uplift-induced residual strain release and late-thrusting extension in the Anaran mountain front anticline, Zagros (Iran)

“…σx may continue to increase at this stage (T 2 ), as documented in several thrust related anticlines (e.g. Tavani et al, 2008Tavani et al, , 2012. This occurs until a certain time T 3 is reached, when uplift causes fast migration of the material towards shallower structural levels.…”

“…the sub-horizontal stress paralleling the tectonic transport direction) progressively increases (e.g. Gray and Mitra, 1993;Holl and Anastasio, 1995;Sans et al, 2003;Tavani et al, 2012). At time T 1 the material has reached its maximum depth before it will be incorporated into the thrust system, implying progressive uplift.…”

“…8B) hosted in exposed km-scale thrust-related folds involving carbonate multilayers, which indicate a pre-to syn-thrusting strike-slip stress regime, at least in the shallower portions of the thrust and fold belt, with the stress field having a subhorizontal σ1 oriented parallel to the regional shortening direction, a near-vertical σ2, and a sub-horizontal and foredeep-parallel σ3 (e.g. Ahmadhadi et al, 2008;Amrouch et al, 2011;Erslev, 2001;Lacombe et al, 2011;Quintà and Tavani, 2012;Tavani et al, 2006Tavani et al, , 2011aTavani et al, , 2011bTavani et al, , 2012.…”