Cenozoic intracontinental deformation pattern of the Himalayan-Tibetan orogen controlled by pre-Cenozoic suture zones and Permian mantle plumes

Abstract:

The Himalayan-Tibetan orogen and Tibetan Plateau have a central north-south width of ~2,000 km, from the Main Frontal Thrust of the Himalaya to the North Qilian Shan frontal thrust-Hexi Corridor foreland basin of northern Tibet. However, the western and eastern parts of the orogen have more complicated geometries, including the Altyn Tagh left-slip fault and the Xianshuihe-Longmenshan faults, that were influenced by the rigid Tarim and Sichuan Basins. We demonstrate how the first-order geometry of this orogen was controlled by pre-Cenozoic suture zones in northern Tibet and Permian mantle plumes that impinged beneath the now-strong Tarim and Sichuan lithospheres. In the Qilian Shan, shortening and exhumation started in the Eocene shortly after the initial India-Asia collision, as supported by new thermochronology. Geologic mapping and geophysical data (i.e., magnetotelluric and seismic reflection) show that deformation in the Qilian Shan exploited the south-dipping early Paleozoic Qilian suture zone, and thus this preexisting weakness was critical for establishing the northern margin of the Tibetan Plateau early in the evolution of the orogen. The pre-Mesozoic geologic history of Tarim Basin is similar to Tibet, and it was not floored by a strong craton since the Precambrian as evidenced by previously documented early Paleozoic shortening beneath the thick Mesozoic-Cenozoic cover. Reprocessed high-resolution magnetic data from Tarim shows a ~300-400 km diameter radial pattern of linear anomalies that we interpret as a remnant Permian (ca. 300-270 Ma) mantle plume head. We hypothesize that the ~30-Myr Permian plume activity resulted in a more viscous, depleted, thicker, dehydrated, and low-density mantle lithosphere. The resulting stronger lithosphere deflected strain around Tarim Basin, including overthrusting in the Pamirs to the northwest and displacement along the Altyn Tagh fault to the northeast, thus shaping the present-day geometry of the Himalayan-Tibetan orogen. Sichuan Basin may have been similarly influenced by the Emeishan plume. Numerical models can recreate the kinematics and geometry of intracontinental deformation in the Himalayan-Tibetan orogen assuming strong cratons and a weak Tibetan lithosphere, and here we present an updated view on exactly how these characteristics were attained.