Title

Documenting metamorphism, deformation, and cooling across Gianbul Dome, Zanskar, NW India

Presenter Information

Meilani Bowman-Kamaha'o

Document Type

Oral Presentation

Location

SURC 201

Start Date

17-5-2012

End Date

17-5-2012

Abstract

The Himalayan Mountains, characterized by high elevations and rapid erosion, are the consequence of continent-continent collision. Although collision is distinguished by contractional deformation, a major extensional fault zone, the Southern Tibetan Detachment System (STDS) trends parallel to the primary contractional fault, the Main Central Thrust (MCT). The channel flow hypothesis (CFH), characterized by a 30km thick, southward flowing channel of ductile mid-crustal rocks bounded above by the STDS and below by the MCT, was developed to explain simultaneous motion on these faults. One prediction of the CFH is the development of gneiss domes, such as Gianbul Dome, that expose mid-crustal rocks within the mountain front. To test the application of the CFH in NW, India this study documents metamorphism, kinematic shear sense, deformation temperatures, and cooling ages across Gianbul Dome. Migmatites in the core of the dome are mantled by decreasing metamorphic grade metapelites and orthogniess, cross cut by generations of leucogranites. Metamorphism reached temperatures and pressures up to 750°C and 8kbar (Robyr et al, 2002). Kinematic shear sense indicators reveal top-down NE in the northeast side of the dome and top-down SW in the southwest. High grade metamorphic minerals grow synchronously with the deformation fabrics, indicating deformation at peak metamorphism. Deformation temperatures decrease from ~700°C across the center of Gianbul Dome to 400°C on the flanks. Near symmetric cooling of the dome below ~400°C occurred at ~19-22 Ma and after formation of the domal geometry. Results indicate that deformation accompanied exhumation from ~700-400°C agreeing in part with the CFH.

Faculty Mentor(s)

Jeff Lee

Additional Mentoring Department

Geological Sciences

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May 17th, 10:40 AM May 17th, 11:00 AM

Documenting metamorphism, deformation, and cooling across Gianbul Dome, Zanskar, NW India

SURC 201

The Himalayan Mountains, characterized by high elevations and rapid erosion, are the consequence of continent-continent collision. Although collision is distinguished by contractional deformation, a major extensional fault zone, the Southern Tibetan Detachment System (STDS) trends parallel to the primary contractional fault, the Main Central Thrust (MCT). The channel flow hypothesis (CFH), characterized by a 30km thick, southward flowing channel of ductile mid-crustal rocks bounded above by the STDS and below by the MCT, was developed to explain simultaneous motion on these faults. One prediction of the CFH is the development of gneiss domes, such as Gianbul Dome, that expose mid-crustal rocks within the mountain front. To test the application of the CFH in NW, India this study documents metamorphism, kinematic shear sense, deformation temperatures, and cooling ages across Gianbul Dome. Migmatites in the core of the dome are mantled by decreasing metamorphic grade metapelites and orthogniess, cross cut by generations of leucogranites. Metamorphism reached temperatures and pressures up to 750°C and 8kbar (Robyr et al, 2002). Kinematic shear sense indicators reveal top-down NE in the northeast side of the dome and top-down SW in the southwest. High grade metamorphic minerals grow synchronously with the deformation fabrics, indicating deformation at peak metamorphism. Deformation temperatures decrease from ~700°C across the center of Gianbul Dome to 400°C on the flanks. Near symmetric cooling of the dome below ~400°C occurred at ~19-22 Ma and after formation of the domal geometry. Results indicate that deformation accompanied exhumation from ~700-400°C agreeing in part with the CFH.