Document Type

Thesis

Date of Degree Completion

Summer 2008

Degree Name

Master of Science (MS)

Department

Geological Sciences

Committee Chair

Jeffrey Lee

Second Committee Member

Wendy Bohrson

Third Committee Member

Charles Rubin

Abstract

Mabja Dome, southern Tibet, exposes mid-crustal rocks proposed to have originated from a southward flowing mid-crustal channel. Kinematic, mean kinematic vorticity (Wm), and metamorphic petrography analyses on these mid-crustal rocks were performed to test this hypothesis. Kinematic indicators show a transition with structural depth from top-north and top-south shear to solely top-south shear. Along the northernmost transects, Wm in schists and orthogneisses range from 0.52–0.84 (63–36% pure shear). Wm for quartzites ranges from 0.9–0.99 (27–1% pure shear). Deformation temperatures increase from ~450 °C in the chloritoid-zone to ~700 °C in the sillimanite-zone and were recorded between ~35–16 Ma. These patterns exhibit a complex flow regime characterized by: (1) opposing shear sense driven by heterogeneous viscosity and/or channel thickness, (2) broad top-south shear along the Main Central Thrust, (3) simple shear partitioned into weaker quartzite horizons, and (4) an increase in lithostatic load with depth.

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