Deformation Kinematics of Main Central Thrust Zone (MCTZ) in the Western Himalayas

• 作者: Mohsin Ahmad Ahanger Ghulam Jeelani
• 来源期刊: 地球科学学刊（英文版）
• 年，卷（期）: 2022,（2）
• 页码范围: 452-461
• 页数: 10页
• 语种: 英文

摘要

The main central thrust (MCT) is one of the major thrusts in Himalayas. In central Hi-malaya, MCT was defined as a contact between underlying Lesser Himalayan Sequence (LHS) and overlying higher Himalayan crystallines (HHC). However, in the Kashmir Himalayas, the main central thrust zone (MCTZ), shear zone associated with MCT, is overlain by Kashmir Tethyan Sequence sug-gesting that the MCTZ has been deformed through a mechanism different than the mechanism respon-sible for MCTZ evolution in other parts of the Himalayas. In the present study we used structural, mi-crofabric and kinematic analyses to investigate the deformation kinematics of MCTZ. Microstructural investigation revealed that the quartz in orthogneiss mylonites of MCTZ was dynamically recrystal-lized by grain boundary migration (GBM) and sub-grain rotation recrystallisation (SGR) with top-to-SW sense of shear. The mean kinematic vorticity number (Wm) just above the thrust ranges from 0.72 to 0.84 (40％–52％ pure shear component) decreasing upwards to 0.65–0.71 (35％–50％ pure shear component). Deformation in the MCTZ is characterized by Rxz strain ratio varying from 2.7 to 8. The present study suggested that the MCTZ suffered 3％–40％vertical shortening and 3％–66％transport-parallel elongation. The results suggested that the HHC ' s were not completely exhumed to the topo-graphic surfaces in the Kashmir Himalayas. Along the basal decollement, i. e., the main Himalayan thrust (MHT), the deformation continued until MCTZ reached the brittle-ductile transition where de-formation mechanism changed to the brittle and the MCTZ rocks were transported to the surface through slip on brittle MCT.