T264 Transformative Science in the Himalaya and Tibet: Insight from Geophysical, Geochemical, and Geologic Studies (Posters)

Wednesday, 3 November 2010
8:00 AM - 6:00 PM
Hall D

KINEMATIC AND TIMING CONSTRAINTS on THE LEO PARGIL SHEAR ZONE: IMPLICATIONS FOR EXTENSION DURING EXHUMATION OF THE LEO PARGIL DOME, NW INDIA

Paper number: T264-3
Program: Technical Sessions
Time: 8:00 AM – 6:00 PM

Authors

Abstract

Orogen-parallel extension is related to exhumation of domes across the southern margin of the Tibetan Plateau, such as the Ama Drime Massif, the Gurla Mandhata Massif, and the Leo Pargil dome. The Leo Pargil dome, NW India, is a 30-km-wide, northeast-southwest striking structure composed of amphibolites facies metamorphic rocks and migmatitic gneiss that are intruded by leucogranite dikes and sills. The dome is bound by oppositely dipping, northeast-southwest trending normal sense shear zones. The northwest-dipping Leo Pargil shear zone on the southwest flank of the dome juxtaposed the high-grade metamorphic rocks and injection complex in the footwall with the overlying metasedimentary rocks to the west during top-down-to-the-west extension followed by brittle top-down-to-the-northwest extension. The Leo Pargil shear zone provides an important opportunity to characterize the development of the solid-state fabric on the southwest flank of the dome.

Mean kinematic vorticity estimates and deformation temperatures from samples of leucogranite, pelitic schist, marble, and quartzite exposed within the Leo Pargil shear zone are integrated with U-Th-Pb analysis on monazite in metamorphic rocks and deformed and undeformed granites from the shear zone to quantify the kinematics and timing of top-down-to-the-west extension.

Deformation temperatures estimated from quartz textures and quartz [c] axis LPOs from rocks within the shear zone suggest that top-down-to-the-west shearing occurred at temperatures from >500 ºC to ~280 ºC. Mean kinematic vorticity estimates from quartzite with a well developed oblique fabric exposed in the shear zone suggests that extension was accommodated by sub-simple shear deformation. A component of pure shear deformation recorded in the rocks indicates that the rocks in the shear zone were thinned during ductile deformation. U-Th-Pb data indicate that rocks exposed within the Leo Pargil shear zone developed a solid-state fabric during top-down-to-the-west extension potentially in the early Miocene.