26 th Himalaya-Karakoram-Tibet Workshop, Canmore, Canada, July 12-13, 2011 Journal of Himalayan Earth Sceinces 44(1) 2011 36 Strain partitioning during dome formation in the Himalaya: Insights into the Ama Drime Massif and Leo Pargil dome, NW India Micah Jessup 1 , Jackie Langille 1 , , John Cottle 2 , Graham Lederer 2 , Talat Ahmad 3 1 University of Tennessee, Knoxville, TN 37996, USA, mjessup@utk.edu 2 University of California, Santa Barbara, CA 93106, USA 3 University of Delhi, Delhi -110007, India Migmatite-cored domes such as Leo Pargil dome (Thiede et al., 2006; Hintersberger et al., 2010), Ama Drime Massif (Cottle et al., 2009; Kali et al., 2010; Langille et al., 2010) and the Gurla Mandhata core complex (Murphy et al., 2002) were exhumed along shear zones that accommodated orogen-parallel extension. These domes are bounded by shear zones that provide snapshots of different stages in the kinematic evolution of the orogen in the transition zone between crustal shortening in the foreland and orogen-parallel extension in southern Tibet. The Ama Drime Massif, Tibet is a north-south trending range that developed during orogen-parallel extension that post-dates (~12 Ma) south-directed extrusion of the GHS. It is bounded by two oppositely dipping shear zones, the Ama Drime detachment (ADD) and Nyonno Ri detachment. The ADD is a west dipping, north-south striking shear zone that juxtaposes upper amphibolite facies migmatitic gneiss in the hanging wall with granulite facies migmatitic gneiss in the footwall. The ADD is a 100-300 m-thick mylonite zone of interlayered quartzite, marble, calc-silicate and leucogranites. Two-feldspar thermometry on asymmetric strain induced myrmekite provides a minimum temperature estimate (370- 435ºC) for top-down-to-the-west sense of shear. Assuming a dip of 30º, these and other estimates of deformation temperature yield displacement estimates of 21-42 km during orogen-parallel extension (Langille et al., 2010). Mean kinematic vorticity estimates, using the rigid grain and quartz grain shape techniques, indicate that early deformation included a high contribution (49-66%) of pure shear (Langille et al., 2010). The Leo Pargil dome, NW India is a northeast striking elongate dome that is composed of a leucogranite injection complex that records protracted melting during the Miocene (Leech, 2008; Langille et al., in prep), potentially synchronous with south-directed extrusion of the GHS. Two oppositely dipping high strain zones, the Leo Pargil shear zone (Thiede et al., 2006) to the northwest and the Qusum shear zone (Zhang et al., 2000) to the southeast, bound the dome. The Leo Pargil shear zone is a zone of distributed (>500 m) deformation that consistently records top-down-to-the-west -northwest sense of shear and juxtaposes amphibolite facies rocks in the footwall with low-grade metasedimentary rocks in the hanging wall. Quartz LPO data from quartzites that are interlayered with leucogranites yield estimates of 500- 650°C while quartz and feldspar textures indicate some overprinting of lower temperature (500-280°C) conditions during exhumation. Exhumation of the Ama Drime Massif occurred during orogen-parallel extension that clearly post-dates south-directed extrusion of the GHS between the STDS and MCTZ. The Leo Pargil dome appears to share a melting history that is similar to the Greater Himalayan Series, but the kinematic link between melting and exhumation during orogen-parallel extension is more complex. The Leo Pargil dome was exhumed from depths near the base of the Tethyan Sedimentary Series by a distributed shear zone. In contrast, the Ama Drime Massif was exhumed from some of the deepest positions that are exposed in the central Himalaya (Cottle et al., 2009; Langille et al., 2010; Kali et al., 2010). References Cottle, J.M., Jessup, M.J., Newell, D.L., Horstwood, S.A., Noble, S.R., Parrish, R.R., Waters, D.J., Searle, M.P., 2009, Geochronology of granulitized eclogite from the Ama Drime Massif: implications for the tectonic evolution of the South Tibetan Himalaya, Tectonics, 28, 1−25. Hintersberger, E., Thiede, R. C., Strecker, M. R., and Hacker, B., 2010, E-W extension in the NW Indian Himalaya, Geological Society of America Bulletin, 122, 1499-1515. Langille, J., Jessup, M., Cottle, J., Newell, D., Seward, G., 2010, Kinematics of the Ama Drime Detachment: Insights into orogen-parallel extension and exhumation of the Ama Drime Massif, Tibet-Nepal, Journal of Structural Geology, 32, 900- 919.