Inferring the Regional Dynamics of Central Songpan-Ganze Terrane Informed by Magnetotelluric Data from the Northern Tibetan Plateau

The central Songpan-Ganze terrane is located in the central northern Tibetan Plateau. It borders the Qaidam Basin to the north, with the Kunlun fault marking their boundary. In the south, it is bounded by the Jinsha suture zone and borders the Qiangtang terrane to the south. A large number of left-lateral strike-slip faults have been mapped within the Songpan-Ganze terrane, showing that the shear strain is distributed over the entire block, and the crust shows the trend of eastward migration. Currently, it is still debated whether the mechanism of crust-mantle deformation and material migration of the Songpan-Ganze region is dominated by the vertical process of asthenosphere upwelling or the horizontal shearing process related to lateral extrusion. To further explore the deep dynamic mechanism, 192 broadband and long-period MT sites collected under the SinoProbe and INDEPTH projects are used to investigate the electrical structure of the crust and upper mantle beneath the central Songpan-Ganze terrane. By processing and analyzing the measured MT data, and using the LBFGS algorithm for three-dimensional (3-D) inversion, a reliable 3-D electrical structure model is derived. The deep electrical structure is analyzed and interpreted by integrating with other background geological and geophysical data. The following preliminary conclusions are drawn:  (1) Under the Ganze-Yushu sinistral strike-slip fault within the Songpan-Ganze terrane, there are a series of low-resistivity channels extending northward in the middle and lower crust, which correspond to the "finger" shaped low-resistivity intrusions under the Kunlun fault, indicating that these "finger" shaped conductors have already been developed within the Songpan-Ganze terrane, and may be related to large-scale sinistral strike-slip deformation in the region. (2) These low-resistivity channels exhibit relatively weak lateral connectivity but demonstrate significant vertical extent, indicating that the deformation mechanisms in the vertical direction within the study area cannot be ignored. This phenomenon is likely closely related to the rheological structure of the block and suggests that the upwelling of mantle-derived thermal materials may play a crucial role in the regional tectonic evolution. (3) The low-resistivity body in the central Songpan-Ganze region gradually narrows from west to east, with its eastern portion exhibiting an upward extension into the upper crust. This may indicate that the Songpan-Ganze terrane experienced heterogeneous stress during the process of accommodating tectonic deformation between the Qiangtang terrane and the Qaidam Basin. As a result, the eastern part of the study area was subjected to greater compressive stress, leading to upward thrusting and the formation of a high-angle thrust conductor.

*This research is funded by The China Magnetotelluric Array (Phase I), National Science and Technology Major Project (2024ZD1000202), Deep Earth Probe and Mineral Resources Exploration - National Science and Technology Major Project (2024ZD1000106-04) and NSFC (42074089).