Middle Crustal Ductile Deformation Patterns in Southern Tibet: Insights from Vorticity Studies in Mabja Dome

Jackie Langille
June 2008

Abstract

Mabja Dome, southern Tibet, exposes mid-crustal rocks proposed to have originated from a southward flowing mid-crustal channel. Kinematic, mean kinematic vorticity (W_m), 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, W_m in schists and orthogneisses range from 0.52–0.84 (63–36% pure shear). W_m 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.

Full Thesis (PDF format)

Digital Commons link: https://digitalcommons.cwu.edu/etd/1418

Update: Jackie was awarded the University's Distinguished MS Thesis award for 2008-2009. Her thesis was published in 2010 in the Journal of Structural Geology [download PDF file].