Space and Time Variability of Detachment‐ Versus Ramp‐Dominated Thrusting: Insights From the Outer Albanides

Abstract

Despite their markedly different structural setting, the northern and southern outer Albanides share a common tectonic evolution from detachment‐dominated to ramp‐dominated, basement‐involved thrusting. The former process (mainly Oligocene to Miocene) is essentially related with the occurrence of a thick décollement level represented by Triassic evaporites, while the latter involves basement ramps splaying out from a middle crustal décollement. As this weak crustal layer is inherited from the Mesozoic rifting stage, the original continental margin architecture is interpreted to strongly influence subsequent convergent deformation. The profoundly different nature of the two dominant décollements in the study area controlled the structural style of the fold and thrust belt. The decoupling capacity of the upper décollement is strongly dependent on the thickness of the Triassic evaporites. Where this is significant (≫1 km; southern outer Albanides), the occurrence of such a thick incompetent layer at the base of competent carbonate units favored the development of break‐thrust folds and imbrication of the sedimentary cover. Fold and thrust belt propagation was instead hindered where original stratigraphic variations resulted in a reduced thickness (≤1 km) of Triassic evaporites. On the other hand, the deeper middle crustal décollement is controlled by basement rheology. Its reactivation during plate convergence was assisted by collision‐related thermal weakening of the crust. This process governed late‐stage (<5 Ma) crustal‐scale tectonic inversion and plays a major role in controlling present‐day seismicity.

Deformation Sequence and Paleofluids in Carbonate Buckle Folds Under Transpression (Pag Anticline, External Dinarides, Croatia)

“…Local shear failure led to localization of compression in conjugate thrusts and other minor structures, which were then involved in folding. This generally occurs in thick competent units (Mazzoli et al., 2022; Morley, 1994; Price & Cosgrove, 1990; Ramsay, 1981). In the northwestward pericline of the Pag anticline, older WNW‐ESE striking, mesoscale thrust fault zones and associated contractional deformation structures are cross‐cut by NW‐SE striking thrusts, backthrusts and fold‐accommodation structures.…”

“…After significant bed rotation fold locking likely produced strain hardening. These structures eventually propagated into thrusts and backthrusts showing high cutoff angles in the fold limbs and into out of syncline thrusts (Mazzoli et al., 2022; Morley, 1994; Price & Cosgrove, 1990; Ramsay, 1981). Fold tightening was also characterized by strike‐slip reactivation of previously formed prefolding and synfolding deformation structures, including conjugate strike‐slip shear fracture arrays, and rotated thrust fault zones.…”

“…In the last decades, fold trains in thrust and fold belts have mostly been interpreted as fault‐related, neglecting the contribution of buckle folding to the regional contraction (Erslev, 1991; Jamison, 1987; Shaw et al., 2005; Suppe, 1983). Kinematic models of fault‐related folds have been extensively applied for estimating the displacement accommodated along blind thrusts for seismic hazard assessment purposes (Dolan & Avouac, 2007), although analogue and numerical modeling, and field studies suggest that a potentially large component of fold growth might be attributed to buckling in addition to slip on the underlying fault (Butler et al., 2018, 2020; Johnson, 2018; Mazzoli et al., 2022). A reliable interpretation of the structural style and partition of the contraction between faulting and folding is therefore crucial for estimating the size of seismogenic sources in thrust and fold belts.…”

“…been extensively applied for estimating the displacement accommodated along blind thrusts for seismic hazard assessment purposes (Dolan & Avouac, 2007), although analogue and numerical modeling, and field studies suggest that a potentially large component of fold growth might be attributed to buckling in addition to slip on the underlying fault (Butler et al, 2018(Butler et al, , 2020Johnson, 2018;Mazzoli et al, 2022). A reliable interpretation of the structural style and partition of the contraction between faulting and folding is therefore crucial for estimating the size of seismogenic sources in thrust and fold belts.…”

Shale 3D Flow and Interaction With Basement Faults in the Niger Delta Deep‐Water Fold and Thrust Belt

“…This results in folding being dominant with respect to thrusting in terms of modes of deformation. Recent studies further suggested that the process of detachment folding is equivalent to that of buckle folding (Butler et al., 2019; Mazzoli et al., 2022). Multilayer buckling is well known to be governed by both viscosity contrasts and thickness of the mechanically dominant competent units (control units sensu Butler et al., 2019) and, more in detail, by the geometrical arrangement and relative thickness of competent and incompetent beds (Ramsay & Huber, 1987).…”