Helium isotopes in hot springs of the Karakorum fault and the Central Pamir: Tracing mantle contributions and tectonic dynamics

Abstract

The over 1000 km long Karakorum fault (KKF) spans along the western edge of the Tibetan Plateau and is a significant geological feature in the western Himalayan–Tibetan orogenic belt. Whereas, the fault's contribution to accommodating the ongoing convergence of the Indian plate and the Asian plate remains fiercely debated. We provided a quantitative study on the helium (He) systematics of springs along the north section of the KKF. The crustal He signature along the Kongur extension system (KES) indicates that it may not be a continuation of the KKF, as the KKF can serve as an ascending channel for deep fluids or/and magma that contain mantle signals but KES cannot. The limited offset of KKF is consistent with continental collision models involving relatively weak crust and distributed deformation. Combined with local magmatic history, existence of high temperature geothermal system, high surface heat flow, and cold India lithosphere mantle beneath the central Pamir, the appearance of mantle-derived He in the northern KKF and Rushan Pshart Suture (RPS) indicates mantle-derived magma chambers in the upper-middle crust. The regional stress condition and ductile middle crust in the south of RPS favor lateral magma propagation, which is in agreement with the observed large north-south span mantle signatures in the springs.