Structural deformation of fold-and-thrust belts is influenced by the properties of décollements (number, rheology, thickness, etc.), the presence of inherited structures in the basement as well as the amount of syntectonic sedimentation, among others. Although the effect of each of these parameters has been well constrained with a series of numerical and experimental works in the literature, few sandbox models comprehensively consider all these parameters together, and particularly investigate the effect of their lateral variation. In this context, we carried out several 3-D sandbox models to investigate the effect of increasing syntectonic sedimentation rate on kinematic evolution of fold‐and‐thrust systems which contain a basal brittle detachment layer and a shallow detachment layer that changed from a brittle to a viscous domain along the mountain strike. The influence of different basement width structures, affecting the kinematics and geometry of the interbedded viscous décollement, has been also tested.Results indicate that the rate of syntectonic sedimentation exerts a first-order control on the kinematic evolution of fold‐and‐thrust belts since increasing syntectonic sedimentation rate stops (in the brittle domain) or delays (in the viscous domain) the propagation of deformation towards the foreland. Moreover, syntectonic sedimentation prohibits the propagation of deformation in the deep décollement level due to the modification of the taper angle. Structural evolution of the transfer zone in between the brittle and viscous domain is also affected since if becomes narrower and more orthogonal to the mountain front at higher sedimentation rates. Specifically, in the brittle domain, the fault dip angle increases with the increase in syn-sedimentation rate and its cross-sectional geometry becomes straighter. In the viscous domain, syntectonic sedimentation affects the partitioning of deformation with development of long-lived and complex 3-D salt structures near the hinterland (such as squeezed diapirs, salt welds and salt tongue), whereas frontal structure becomes more cylindrical. Toward the hinterland, syntectonic sedimentation increases backthrust activity, which becomes increasingly different between the brittle and viscous domain. For instance, the increase in backthrust displacement in the ductile domain is greater than the one in the brittle domain. About the basement high, our study reveals that it has a strong controlling effect on the viscous domain, dominating the development of structural belt on the top of the basement high and promoting the propagation of deformation front to the pinch-out of the salt layer. Besides, syntectonic sedimentation simplifies the structural style between the basement high and the hinterland. It strengthens the structural influence of the transfer zone, which localizes into a single strike-slip transfer fault which increases the frontal fault displacement.Our experimental results are compared with structures in the Wushi-Kuqa fold-and-thrust belts in Southern Tianshan (Central Asia) and help better understanding interaction between syntectonic sedimentation, décollement properties and basement configuration.
Abstract Tectonic evolution models for the Cretaceous Russia Sikhote‐Alin and eastern NE China continental margin and interior remain controversial. To understand the magmatic evolution over time and assess regional geodynamic processes, we sampled a diverse array of igneous rocks and employed zircon U‐Pb dating, hornblende and plagioclase 40 Ar‐ 39 Ar dating, whole‐rock major and trace element analysis, and 87 Sr/ 86 Sr and 143 Nd/ 144 Nd isotopic analysis. The west Sikhote‐Alin Pikeshan Formation volcanics and associated granites occurred at a peak of ~118 Ma and are hosted by the Triassic‐Jurassic accretionary complex. Their whole rock geochemistry shows that SiO 2 increased in a linear trend, Eu/Eu* values decreased from 0.91 to 0.38, and ε Nd ( t ) values decreased from +0.6 to −2.9, indicating magma mixing of a juvenile mantle wedge source and continental crust, consistent with a continental arc. The arc thickened over time with a felsic dike hosted in the Pikeshan granites showing depletion in heavy rare earth elements. The termination of the arc front is documented by the ~107‐Ma intermediate lamprophyre and felsic dikes with ε Nd ( t ) values of +4.5 to +1.1, indicating an increased mantle contribution over time. Lithospheric extension of the Jiamusi Block to the west occurred at ~100 Ma, characterized by bimodal volcanism and composite dike emplacement, suggestive of asthenosphere upwelling. Based on the spatial and temporal distribution of these igneous rocks, the continental arc and intraplate magmatism migrated eastward contemporaneously. We favor a model invoking rollback of the subducting Paleo‐Pacific slab affecting a long‐lived continental arc.
Abstract The Cenozoic North Altyn Fault (NAF) is a major splay of the Altyn Tagh Fault along the northwestern margin of the Tibetan Plateau, but its role in the development of this plateau margin in response to the India‐Eurasia collision is highly debated. Here, we investigate fault geometry, kinematics, and shortening magnitude along the westernmost 120 km of the NAF. Seismic surveys reveal minimal Cenozoic shortening in the subsurface of the Southeast Tarim Basin and support for large‐scale (>120 km) left slip on the NAF. Based on the satellite imagery, two new faults are identified to define the northern boundary of the NAF system, which together with the NAF to the south constitute a narrow transpressional shear zone comprised of three basement‐cored, fault‐bound slivers. Fission track data and thermal modeling indicate that the NAF zone experienced broad reburial during early Cenozoic that was locally interrupted by ∼40 to 35 Ma exhumation proximal to the NAF, followed by widespread but heterogeneous exhumation since ∼17 to 15 Ma associated with ∼9 to 11 km of total shortening across the NAF system via thick‐skinned faulting. We conclude that the NAF initiated as a left‐slip fault at ∼40 to 35 Ma and then became transpressional at ∼17 to 15 Ma during the middle‐Miocene reorganization of the Altyn Tagh Fault system. We find no evidence to support prior inferences of large‐scale (∼100 km) underthrusting of the Tarim Basin beneath the Tibetan Plateau along the NAF.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)