Structural analysis of the Gaurishankar Lineament to understand its role as a cross fault in the east-central Nepal Himalaya

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Date

2023

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Montana State University - Bozeman, College of Letters & Science

Abstract

The Gaurishankar Lineament (GL) in east-central Nepal is a topographic feature in eastern Nepal that has been proposed to be a cross-fault (faults perpendicular to the regional E-W strike). This feature has also been proposed to have blocked the lateral propagation of the thrust rupture that was activated during the Mw 7.8 Gorkha earthquake. To understand whether the GL is a cross fault, I conducted a field study along ~E-W traverses south of Gaurishankar peak in the Rolwaling (Greater Himalayan Sequence (GHS)) and in the central Tamakoshi and Jiri regions (Lesser Himalayan Sequence (LHS)). I augmented my fieldwork with petrographic and kinematic analysis of oriented samples. As circumstantial evidence for the GL representing the topographic expression of a cross fault, I identified multiple steep fracture patterns orthogonal to regional E-W striking fabric in the Rolwaling region and an additional system of NW striking fabric orthogonal to the NNE trending GL. In the Jiri region, the offset in a thin band of graphitic schist within the rocks of the LHS aligns along the GL and may represent part of a cross-fault system. An eastward plunging synclinal fold that covers the broad region between Tamakoshi and Jiri is disrupted to the east along the GL, also consistent with the presence of a cross fault. Several NW striking faults in the Jiri region end along the GL, as suggested by the topographic expression from the satellite imagery. Further study is needed to recognize and develop a comprehensive understanding of the GL as a cross fault and to explore a newly identified system of NW striking fault.

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