T285 Transformative Science in the Himalaya and Tibet: Insight from Geophysical, Geochemical, and Geologic Studies

Wednesday, 3 November 2010
1:30 PM - 5:30 PM
Mile High Ballroom 2AB/3AB

STRAIN PARTITIONING AND CRUSTAL MELTING WITHIN THE LEO PARGIL DOME, NW INDIA

Paper number: T285-6
Program: Technical Sessions
Time: 2:50 PM – 3:05 PM

Authors

Abstract

Dome complexes along the transition between the Tibetan plateau and the crest of the Himalaya provide insight into tectonic processes that were active at different positions in the mid-crust during various stages in the evolution of the orogen. The central portion of some domes are dominated by intrusion complexes of sills and dikes of leucogranite that record the migration and concentration of partial melt during deformation and crustal-scale flow. The margins of the domes record a transition from melt-present deformation to solid-state fabric development reflecting the onset of progressively lower temperature deformation mechanisms during exhumation. Field-and lab-based data from these domes help to identify the interactions between melting, metamorphism and strain partitioning during early stages of mid-crustal flow and subsequent exhumation. These data are an essential test of competing kinematic and thermomechanical models of dome formation on the southern margin of the Tibetan plateau and are also relevant to understanding the evolution of collisional orogens in general.

The Leo Pargil dome (LPD), NW India is a NNE striking, 30-km-wide elongate structure bounded by the Leo Pargil shear zone (LPSZ) to the west and the Qusum fault to the east that was exhumed within a zone bounded by the South Tibetan detachment system to the south and the Karakoram fault to the north. Preliminary data indicate that the rocks in the hanging wall of the LPSZ reached 650ºC and 0.7 GPa during the Oligocene. Migmatitic gneiss at deeper structural positions was the likely source region for an extensive, multi-phase injection complex (26-16 Ma) at shallower structural positions that preceded rapid exhumation of footwall rocks. During exhumation strain was partitioned into the LPSZ that consistently records top-down-to-the west/northwest sense of shear at deformation temperatures >500ºC.