Lithospheric Deformation and Active Tectonics of the NW Himalayas, Hindukush, and Tibet

Ishtiaq A K Jadoon,Zahid I Bhatti,Saif-Ur-Rehman K Jadoon,Syed T H Shah,Lin Ding,Muhammad Qasim,Songjian Ao

doi:10.2113/2021/7866954

Abstract

AbstractThe Himalayan Mountain System (HMS) and the Tibetan Plateau (TP) represent an active mountain belt, with continent-continent collision. Geological and geophysical (seismological modeling, seismic reflection, and gravity) data is reviewed herein for an overview of the lithospheric deformation and active tectonics of this orogen. Shallow crustal deformation with dominance of thrusting along the margins of the TP is interpreted with normal faulting in the center and strike-slip deformation with the lateral translation of blocks, over a wedge of ductile deformation. The seismicity is the linear concentration over the margins of the orogen to ~20 km depth with exception of the Hindukush and Pamir having seismicity to 300 km depth with an interpretation of sinking Indian and Asian lithospheres. The lithospheric structure is represented by mechanically weak surfaces representing décollement to 15 km depth over the basement, low-velocity zone (LVZ) at ~20 km, the Moho at ~40-82 km, and the lithosphere-asthenosphere boundary (LAB) at 130-200 km depth. The décollement, termed as the Himalayan Mountain Thrust (HMT), is inferred to be rooted at the base of the Moho in central Tibet. Along this fault, brittle crustal deformation is interpreted to ~15-20 km depth, with brittle-ductile deformation along LVZ and ductile slip with crustal duplexing along the lower crust. The mantle lithosphere of the Indian plate is inferred as duplicated with the wedging of the Asian mantle lithosphere. The active tectonics of the TP is proposed to follow the mechanics of thrusting, similar to the foreland deformation of the mountain belts and accretionary prisms.

Highlights

The Himalayan Mountain System (HMS) and the Tibetan Plateau (TP) represent the world’s highest and biggest active mountain belt, with an advanced stage of the continent-continent collision between Indian and Eurasian plates (Figure 1)
Our model suggests the presence of an anticlinal stack with duplexing of (1) lower crust and (2) lithospheric mantle of the Indian/Tibetan plates between the low-velocity zone (LVZ), Moho, and lithosphere-asthenosphere boundary (LAB)
(1) Brittle deformation to a shallow ~20-25 km depth is interpreted in the HMS and the TP, whereas ductile deformation is interpreted below LVZ at ~20-25 km and LAB at 200 km depth

Summary

Introduction

The HMS and the TP represent the world’s highest and biggest active mountain belt, with an advanced stage of the continent-continent collision between Indian and Eurasian plates (Figure 1). Surface geological (such as magmatism, metamorphism, and deformation) [10,11,12] and subsurface geophysical studies based on gravity modeling [5, 13, 14], seismicity (Figure 2; [2, 5, 6, 15,16,17]), seismic reflection interpretations [18, 19], and seismic tomography [4, 20,21,22] have improved our understanding about the structure, deformation, and evolution of the HMS and the TP. The geological and geophysical data is integrated for review and a better understanding of (1) active tectonics, (2) lithospheric structure and deformation, and (3) evolution of the TP to provide a framework for overall understanding of the orogen and future studies

Geological Background

General Observations and Interpretations

Magnitudes 6

Findings

Discussion

Conclusions