HR: 0800h
AN: V41C-0728    [Abstracts]
TI: 21 Ma Eclogite From the Main Central Thrust Sheet, Eastern Nepal Himalaya
AU: * Corrie, S L
EM: staceycorrie@mail.boisestate.edu
AF: Department of Geological Sciences, Boise State University, Boise, ID 83725, United States
AU: Kohn, M J
EM: mattkohn@boisestate.edu
AF: Department of Geological Sciences, Boise State University, Boise, ID 83725, United States
AU: Vervoort, J D
EM: vervoort@wsu.edu
AF: School of Earth and Environmental Sciences, Washington State University, Pullman, WA 99164, United States
AU: Parkinson, C D
AB: Though uncommon throughout the Himalaya, eclogites have been documented in the Kaghan Valley of Pakistan, the Tso Morari dome in India, the Kharta region of Tibet, and the Makalu-Everest region of the Arun River valley in eastern Nepal. The Kaghan and Tso Morari UHP eclogites have been dated at ~50 Ma, and are commonly viewed as reflecting aborted subduction of the leading edge of the Indian plate during the initial stages of Indo- Asian collision. Here we show that the Arun eclogites are significantly younger, only ~21 Ma, so reflect either different origins, or substantial time lags in tectonics along strike. The Arun eclogites are stratigraphically continuous with the surrounding Greater Himalayan Sequence (GHS) felsic gneisses, and have been interpreted as metamorphosed basaltic sills. P-T conditions have been estimated at >14 kbar at 670-710 °C. The GHS in this region overlies Lesser Himalayan rocks along the Main Central Thrust (MCT), which can be traced for over 2000 km along strike. Lu-Hf dates from garnet separates in one relict eclogite indicate an age of 20.7±0.4 Ma (MSWD = 2.2). Five garnet amphibolites from nearby were also dated via Lu-Hf, and their ages range from 14-20 Ma (13.9±2.5, 14.1±0.3, 14.5±2.8, 15.1±0.6, and 19.8±1.1 Ma). The ~21 Ma age obtained from the eclogite postdates eclogite ages from the western Himalaya (Kaghan and Tso Morari) by ~30 Myr, and has important implications for tectonic models of Himalayan orogenesis. One possible model is that (aborted) subduction, slab breakoff, and ascent of India's leading edge occurred diachronously: ~50 Ma in the western Himalaya, ~20 Ma in eastern Nepal, and presumably even younger in the eastern Himalaya. Alternatively, because the Arun eclogites did not reach ultra-high pressure conditions seen by western eclogites (only ≥45, not ≥90 km depth), they may simply reflect deepening or longer transport of the MCT in the Arun area. Regardless, a ~21 Ma age for these eclogites combined with several 14-15 Ma ages for nearby garnet amphibolites implies young initial movement on the MCT at Arun, as late as 14 Ma.
DE: 8400 VOLCANOLOGY
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting