The Miocene tectonic transform of the South Tibetan Detachment System (STDS), eastern Himalayan

The compressional collision between the Indian and Eurasian plates has formed an extensive continental deformation zone and the Himalayan orogen belt, generating several east-west trending giant fault zones. Among these predominantly thrust fault zones, the South Tibetan Detachment System (STDS) is the only normal fault, extending over 2000 kilometers, and thus has become the largest single existing detachment fault system in the world . The STDS sharply separates the shallow un-metamorphosed or weakly metamorphosed Tethyan Himalayan Sequence (THS) from the deep high-grade metamorphosed, partially melted Greater Himalayan Crystalline Complex (GHC). The emergence of the STDS has revised the traditional view that compression and extension cannot coexist. During the entire Himalayan orogenic process, it has played a crucial controlling role in mountain uplift, the exhumation of high-grade metamorphic rocks at the root of the orogen, and the formation and migration of leucogranites. With the advancement and widespread application of high-pressure experiments, phase equilibrium simulation calculations, EBSD fabric analysis, and in-situ trace element-isotope dating techniques, significant progress has been achieved in STDS research, while new questions have also been raised. This study systematically reviews the new progress and existing controversies regarding the STDS and the Himalayan orogenic process, covering key aspects such as the active period of the STDS, genetic mechanisms, its relationship with leucogranites, and the geometry and kinematics of the Tethyan Himalayan D′ecollement (THD). By using multi-isotopic geochronology, the activity period of THD is determined, which further restricts the transition time from the southward movement of THD to the northward movement of STDS.

Acknowledge

This work was supported by the Deep Earth Probe and Mineral Resources Exploration - National Science and Technology Major Project (Grant No. 2024ZD1001006) and the National Natural Science Foundation of China (Grant No. 42472285, U2444202) and the Basic Research Fund of the State Key Laboratory of Deep Earth and Mineral Exploration (JKYDM2025203).