The highest mountains on Earth were pushed up by the collision of the Indian subcontinent with Asia. This violent continental collision caused the crust to double in thickness. Localized extension in the upper crust allows partially molten middle crust to upwell, forming Himalayan gneiss domes tens of kilometers across. My research in Ladakh (northern India) sheds light on the links between heating in the middle crust, deformation, and gravitational collapse in the Himalayas.
Accessory minerals including zircon, monazite, and titanite preserve critical information about heating events in Himalayan rocks. I performed split-stream laser ablation ICP-MS analyses of these minerals to determine the timing and duration of high temperature metamorphism. Simultaneous measurement of U-Pb isotopes and trace elements allowed me to link metamorphism to radiometric dates.
Our work suggests that preexisting granite plutons may have acted as relatively rigid megaboudins and played an important role during exhumation. Also, positive feedbacks among heating, melting, and positive buoyancy facilitated ductile doming of the middle crust. This process was coeval with gravitational collapse of the overthickened continental crust around 20 million years ago.
For more information about my Himalaya research, see my publications:
Horton, F., Lee, J., Hacker, B., Bowman-Kamaha'o, M, Cosca, M., 2014, Himalaya gneiss dome formation in the middle crust and exhumation by normal faulting: New geochronology of Gianbul dome, northwestern India: GSA Bulletin, v. 126, B31005.1.
Horton, F., Leech, M.L., 2013, Age and origin of granites in the Karakoram shear zone and Greater Himalaya Sequence, NW India: Lithosphere, v. 5, p. 300–320.
For information about ultrahigh-temperature metamorphism in continental collision zones, see my research page about radiogenic heating in Madagascar.