Quartz microstructures and crystallographic preferred orientation analysis across the Himalayan metamorphic core reveal exhumation through changing taper angle and strain partitioning along discreet fault zones

Abstract

The Himalayan metamorphic core in the Bhagirathi Valley of North India comprises three major tectonic zones: the Main Central Thrust zone (MCTz) that separates the Paleoproterozoic Lesser Himalayan Crystalline rocks from the Proterozoic to Cambro-Ordovician Greater Himalayan Sequence; the High Himalayan Discontinuity (HHD) that separates the lower inverted metamorphic sequence from the upper anatectic part of the GHS; and the Jhala Normal Fault (JNF) that marks the northernmost boundary of this metamorphic core. Quartz microstructural analyses across this metamorphic core indicate that dynamic recrystallization at lower temperatures overprinted the high-temperature deformation features, also evident from dominant prism<a> slip in quartz. Strength of quartz crystallographic preferred orientation (CPO) is also highest at these locations. Vorticity analysis suggests simple shear partitioning in the JNF and MCTz, with pure shear in other parts. It is concluded that the exhumation of the Himalayan metamorphic core was facilitated by simple shear along the JNF and MCTz, with thrust propagation south of MCTz compensating for changes in the taper angle of the Himalayan wedge due to activity along the JNF.