Lower Crustal Rheology Controls Strain Partitioning and Mode of Intracontinental Deformation

The factors that control strain partitioning along plate boundaries and within continental interiors remains poorly resolved. Plate convergence may be accommodated via distributed crustal shortening or discrete crustal-scale strike-slip faulting, but what controls these differing modes of deformation is debated. Here we address this question by examining the actively deforming regions that surround the Tarim Basin in central Asia, where deformation is uniquely partitioned into predominately strike-slip faults in the east and distributed fold-thrust belts in the west to accommodate Cenozoic India-Asia plate convergence. We present integrated geological and geophysical observations to elucidate patterns in crustal deformation and compositional structure in and around the Tarim Basin. The thrust-dominated western Tarim Basin correlates with a strongly-magnetic lower crust, whereas strike-slip faulting along the eastern margins of the Tarim Basin lack such magnetic signals. We suggest that the lower crust of the western Tarim is more mafic and stronger than in the east, which impacts intra-plate strain partitioning. A stronger lower crust results in vertical decoupling to drive mid-crust horizontal detachments and facilitate thrust faulting, whereas a more homogenized crust favored vertical transcrustal strike-slip faulting. These rheological differences likely originated from the impingement of the Permian Tarim plume focused in the west. A comparison with the Longmen Shan of eastern Tibetan Plateau reveals remarkably similar strain partitioning that correlates with variations in foreland rheology. Our results highlight how variations in lower-crust viscosity impact strain partitioning in an intra-plate setting and how plume processes exert a strong control on later continental tectonic processes.