Sinistral transpression along the Main Boundary Thrust in Amritpur area, Southeastern Kumaun Himalaya, India

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• 作者：Jyoti Shah^a ; Deepak C. Srivastava^a ; ^{dpkesfes@iitr.ernet.in} ; ^{dpkesfes@gmail.com} ; Suman Joshi^b
• 关键词：Main Boundary Thrust ; Fault zone ; Imbricate structure ; Paleostress ; Transpression ; Strain partitioning
• 刊名：Tectonophysics
• 出版年：2012
• 期刊代码：82_00401951
• 类别：ear
• 出版时间：6 April, 2012
• 卷：532-535
• 期：Complete
• 页码：258-270
• 文件大小：5451 K

摘要

Outcrop mapping and structural analyses in a 100 m thick fault damage zone elucidate geometry and kinematics of the Main Boundary Thrust in the study area. The north-dipping fault damage zone is sandwiched between the Proterozoic Amritpur granite in the hangingwall and the Neogene Siwalik sediments in the footwall. The Amritpur granite is overlain by the volcanic-sedimentary sequence along a top-to-the-south thrust. The footwall sediments are deformed into gentle upright and steeply-plunging folds. By contrast, the hangingwall granite is generally massive. The km-scale folds in the Sub Himalayan sediments are geometrically discordant to the folds in the Lesser Himalayan volcanic-sedimentary sequence.

The damage zone contains both the Sub Himalayan sediments and the Lesser Himalayan amphibolite. It consists of an imbricate structure, tectonic wedges and pressure solution bands. The imbricate structure is made up of seven fault-bounded lithotectonic domains that record the imprints of coaxial refolding and subsequent modification of the folds into sheath-like structures. The geometry and kinematics of mesoscopic structures and the results of paleostress analysis reveal a sinistral wrench accompanied N-S to NNE-SSW directed subhorizontal shortening in the damage zone. The aforesaid evidences also help distinguish between pure contractional, pure wrench, contraction-dominated and wrench-dominated deformation in the different domains and the tectonic wedges. The sinistral transpression in the damage zone is ascribed to the occurrence of an oblique/lateral ramp along the Main Boundary Thrust in the study area.