HR: 0800h
AN: T31D-0668    [Abstracts]
TI: Early Miocene granitoids from the Leo Pargil gneiss dome, northwest Himalaya
AU: * Hassett, W
EM: whassett@sfsu.edu
AF: San Francisco State University, Department of Geosciences, 1600 Holloway Avenue, San Francisco, CA 94132, United States
AU: Leech, M L
EM: leech@sfsu.edu
AF: San Francisco State University, Department of Geosciences, 1600 Holloway Avenue, San Francisco, CA 94132, United States
AB: The Leo Pargil gneiss dome is comprised of upper amphibolite-facies metasedimentary rocks of the lower Tethyan Himalayan sequence (known as the Haimantas Group), that are intruded by numerous small granitoid bodies and leucogranite dikes. The dome is located in northern India/southwestern Tibet at the junction of the Sutlej and Spiti rivers, west of the Zada basin. U-Pb SHRIMP dating of zircon yield concordant ages ranging from Late Archean to Late Proterozoic for paragneisses (2.6 Ga to 970 Ma) corresponding to the Haimantas group, and Early Oligocene to Middle Miocene ages for granitoid intrusions (33 Ma to 15 Ma). Concordant analyses and lower intercept ages from Tera-Wasserburg concordia plots range from 28.1-17.2 Ma. Late Oligocene to Early Miocene ages are from zircon domains with consistently high U contents (1500 to over 25000 ppm). Linear regression of age vs. U content scatter plots show a trend toward younger ages (22-20 Ma) corresponding to ages from zircon with lower U contents (1000-3000 ppm) and that is consistent with lower intercept ages. These Early Miocene ages for Leo Pargil granitoids correspond to the ages for the widespread leucogranite bodies exposed throughout the Himalaya and granites from the North Himalayan gneiss domes further east.
DE: 1040 Radiogenic isotope geochemistry
DE: 1115 Radioisotope geochronology
DE: 8178 Tectonics and magmatism
DE: 9320 Asia
SC: Tectonophysics [T]
MN: 2007 Fall Meeting