Control of crustal strength, tectonic inheritance and extrusion stretching/indentation shortening rates on crustal deformation and basin reactivation: insights from laboratory models

Geological settings characterized by the simultaneous action of multiple (cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58) multiple coeval (cid:58) tectonic regimes provide a unique opportunity to understand complex interactions among different geodynamic processes. From an experimental point of view, these contexts (cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58) However, (cid:58)(cid:58)(cid:58)(cid:58) they remain comparatively less studied (cid:58)(cid:58)(cid:58)(cid:58) from (cid:58)(cid:58) an (cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58) experimental (cid:58)(cid:58)(cid:58)(cid:58) point (cid:58)(cid:58) of (cid:58)(cid:58)(cid:58)(cid:58)(cid:58) view than areas with more simple patterns of deformation resulting from primary plate-boundary interactions. Here, we carried out analog experiments involving simultaneous shortening and orthogonal extension under different rheological conditions, and including the effect 5 of crustal inheritance. We performed brittle experiments and brittle-ductile experiments to simulate cases of “strong” and “weak” crusts, respectively. We present two types of experiments: i) one stage (cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58) one-stage (cid:58) experiments with either shortening-only or synchronous orthogonal shortening and stretching, and ii) two stages (cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58) two-stage (cid:58) experiments with a ﬁrst phase (cid:58)(cid:58)(cid:58)(cid:58) stage of stretching and a second phase (cid:58)(cid:58)(cid:58)(cid:58)(cid:58) stage with either shortening-only or synchronous orthogonal shortening and stretching. In our models, deformation occurs (cid:58) is (cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58) accommodated by a combination of normal, thrust, and strike-slip faults with structures location depending on boundary conditions and crustal inheritance. For brittle models, we show that the three types of structures can develop at the same time for intermediate ratios of extrusion over indentation (cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58) stretching (extension) over shortening rates (1.4< V e / V s <2). For ratios, deformation is accommodated by in the of model. We also show that extensional structures formed during a ﬁrst stage of deformation are never inverted under orthogonal shortening but can be reactivated as normal or strike-slip faults depending on V e / V s . The models replicate some deformation patterns documented in nature. Independently of the crustal rheology or the presence of crustal weaknesses, conjugate strike-slips faults develop along with variable structures from compressional structures to the south . An analysis of the stress state suggests that different tectonic regimes are found within the model: extensional tectonic regime where σ 1 is vertical, wrench (strike-slip) regime where σ 2 is vertical and compression regime where σ 3 is vertical 1905) structures to (cid:58)(cid:58)(cid:58) the north. The transition from one regime to another therefore results from the permutation of one of the horizontal principal stress axes with the vertical one, controlled by the relative magnitude between the principal stresses as described by b = ( σ 2 − σ 3 ) / ( σ 1 − σ 3 ) . A change from extensional to wrench regime is favored for high b values while a change from wrench regime to compression b values. strength of the crust, its past deformation history and the relative ratio of extrusion rate over indentation stretching rate shortening rate, both normal faults and thrust faults remain with similar orientations, i.e. N-S and W-E E-W, respectively. Instead, strike-slip faults exhibit a wide wider range of possible orientations with respect to the indentation (or extrusion shortening (or (cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58) stretching) direction. As such they could give us insights into the tectonic context in which they formed. In particularwide angle conjugate , (cid:58) strike-slip faults (with angles of up to ∼ 65 ◦ with respect to indentation direction ) N-S 6B, 6C and (cid:58)(cid:58)(cid:58) 6D). These results differ from previous basin inversion analog models by Del Ventisette et al. (2006); Sani et al. (2007); Deng et al. (2020), which also applied a basin-parallel shortening after a ﬁrst stage of orthogonal extension. In these models, despite the high obliquity low (cid:58) angle between basin strike and shortening direction, thrust 525 faults formed parallel or at a low angle with the shortening direction, ultimately producing basin inversion. A difference in This difference could result from the boundary conditions applied in our models BI08-11 and CE 17-20, where active orthogonal extensiontook place during shortening, shortening is /V s is ≥ 0.9 and the three regimes operate simultaneously when V e /V s is ≥ 1.4, possibly indicating a minimum value in this ratio for effective lateral scape (cid:58)(cid:58)(cid:58)(cid:58)(cid:58) escape (cid:58) to take place. Independently of the crustal rheology or the presence of crustal weaknesses, we observe the development of conjugate strike-slips (cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58) strike-slip faults accompanied by variable normal faulting during compression/indentation (cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58)(cid:58) shortening. This is reminiscent of those structural systems seen in nature accommodating tectonic escape of crustal blocks in Central Asia, eastern Alps, eastern Anatolia, and the Tibetan plateau. Our results indicate that the conjugate strike-slip systems are favored by an overall weaker crust, which is consistent with observations in the former orogenic areas. In models that include an initial phase stage of extension, we observe variable degrees of extensional to strike-slip reactivation of the previous extensional basins during basin-parallel shortening that are compatible with Late Mesozoic examples in the San Jorge basin in Patagonia and the Baikal rift.