Differential late-Cenozoic uplift across the Dongjiu-Milin Fault Zone in the Eastern Himalayan Syntaxis revealed by low-temperature thermochronology

Abstract

The Eastern Himalayan Syntaxis (EHS), as one of the most tectonically active regions on the Earth, is one of the best places to explore the relationship between tectonics and surface exhumation process. The uplift and exhumation history are often by one of two leading models: a stationary or localized “tectonic aneurysm” or a northeasterly “migrating crustal antiform”. Previous researchers have placed great emphasis on the core zone of Namche Barwa antiform. However, the Dongjiu-Milin Fault Zone (DMFZ), which forms the northwestern boundary of the antiform and plays an important role for deformation process in the EHS, is still poorly understood. In this study, we focus on differential late-Cenozoic uplift across the DMFZ. We collected 10 bedrock samples in two vertical transects, one on the northwest side of the DMFZ on the Lhasa block and one on the southeast side on the Namche Barwa antiform, and conducted apatite fission track and zircon fission track analyses. Ten samples collected from the two vertical transects yield AFT ages between 3.2 million years ago (Ma) and 10.3 Ma and ZFT ages between 9.9 Ma and 12.9 Ma. A finite-element analysis reveals that the two sides of the DMFZ have undergone quite different uplift histories and processes in the late-Cenozoic: The Lhasa block is uniformly uplifted, while the Namche Barwa antiform is nonuniformly uplifted similar to a buckle fold. The phenomenon revealed in this study is best explained by a mechanism whereby the EHS is characterized by the northeasterly migration of an antiform.