Timing of slip across the South Tibetan detachment system and Yadong–Gulu graben, Eastern Himalaya

Abstract

The Yadong–Gulu graben preserves the kinematic and temporal relationships between east–west-directed extension in southern Tibet and north–south extensional strain in the Himalaya. In the Yadong region, distinct outer and inner top-down-to-the-north segments of the South Tibetan detachment system (STDS) are recognized. Herein, we combine high- to medium-T (U–Pb, 40Ar/39Ar) and low-T (apatite fission-track, apatite (U–Th)/He and zircon (U–Th)/He) thermochronometry to investigate the timing of slip across the STDS and Yadong–Gulu structures. These data demonstrate that the cessation of the Yadong shear zone, the structurally outer ductile segment of the STDS, occurred c. 20 Ma and that motion along the inner brittle–ductile Zherger La detachment continued after c. 16.6 Ma, ending by 11 Ma. The cooling history in the immediate STDS footwall is characterized by two main episodes of relatively rapid cooling and exhumation. The first occurred in the middle Miocene (c. 15–11 Ma), and is common along-strike of the innermost STDS footwall, related to cooling of the STDS. The second occurred in the late Miocene–Pliocene (c. 7–3 Ma), and is local to the Yadong–Gulu graben footwall in NW Bhutan, indicating that late Miocene–Pliocene slip along the graben system contributed to exhumation of the STDS east of the graben rift.Supplementary material: Tables of analytical data, dating results, and input data and model parameters of HeFTy are available at https://doi.org/10.6084/m9.figshare.c.5132941