Title

Mountain Building in The Greater Himalayan Range, India: Insight from Metamorphic, Kinematic, and Deformation Temperature Studies

Presenter Information

Jon Stordahl

Document Type

Oral Presentation

Location

SURC Ballroom A

Start Date

17-5-2012

End Date

17-5-2012

Abstract

My research tests two different hypotheses to explain the unusual processes of extensional faulting, during continent-continent collision, and mountain building in the Zanskar Valley, Greater Himalayan Range, India. Exposures of mid-crust rocks (up to 30km deep) are exhumed to the surface by either channel flow (ductile) or gravitational collapse (brittle) mechanisms beneath the Zanskar normal fault (ZNF). The former mechanism predicts high temperatures (~350-650°C) and ductile deformation of rocks, whereas the latter predicts relatively low temperatures (≤300°C) and brittle deformation. Rocks exposed beneath the ZNF display diagnostic metamorphic minerals garnet, kyanite and sillimanite, indicating these rocks were at temperatures and pressures as high as ~650°C and 6-8 kbars. Most rocks possess kinematic (sense of displacement) deformation features such as shear bands indicating regional extensional exhumation to the SW from beneath the ZNF. Quartz microstructures in samples record a temperature range from ~375°C at the fault surface, increasing to ~650°C at the deepest structural levels sampled (~10km beneath the fault). Microscopic analyses of samples documents the coeval relationship between the formation of metamorphic minerals, kinematic indicators, and quartz microstructures indicating high temperature ductile deformation during exhumation. This research provides evidence for the presence of a compressed geothermal gradient of approximately 100°C/km beneath the ZNF, well in excess of a normal gradient of ~30°C/km. A geothermal gradient of this magnitude cannot be associated with gravitational collapse but provides evidence that ductile thinning of the hot mid-crustal rocks and exhumation, via channel flow, are responsible for mountain building processes in the region.

Poster Number

4

Faculty Mentor(s)

Jeffrey Lee

Additional Mentoring Department

Geological Sciences

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May 17th, 2:00 PM May 17th, 4:30 PM

Mountain Building in The Greater Himalayan Range, India: Insight from Metamorphic, Kinematic, and Deformation Temperature Studies

SURC Ballroom A

My research tests two different hypotheses to explain the unusual processes of extensional faulting, during continent-continent collision, and mountain building in the Zanskar Valley, Greater Himalayan Range, India. Exposures of mid-crust rocks (up to 30km deep) are exhumed to the surface by either channel flow (ductile) or gravitational collapse (brittle) mechanisms beneath the Zanskar normal fault (ZNF). The former mechanism predicts high temperatures (~350-650°C) and ductile deformation of rocks, whereas the latter predicts relatively low temperatures (≤300°C) and brittle deformation. Rocks exposed beneath the ZNF display diagnostic metamorphic minerals garnet, kyanite and sillimanite, indicating these rocks were at temperatures and pressures as high as ~650°C and 6-8 kbars. Most rocks possess kinematic (sense of displacement) deformation features such as shear bands indicating regional extensional exhumation to the SW from beneath the ZNF. Quartz microstructures in samples record a temperature range from ~375°C at the fault surface, increasing to ~650°C at the deepest structural levels sampled (~10km beneath the fault). Microscopic analyses of samples documents the coeval relationship between the formation of metamorphic minerals, kinematic indicators, and quartz microstructures indicating high temperature ductile deformation during exhumation. This research provides evidence for the presence of a compressed geothermal gradient of approximately 100°C/km beneath the ZNF, well in excess of a normal gradient of ~30°C/km. A geothermal gradient of this magnitude cannot be associated with gravitational collapse but provides evidence that ductile thinning of the hot mid-crustal rocks and exhumation, via channel flow, are responsible for mountain building processes in the region.