HR: 1340h
AN: V43A-1555    [Abstracts]
TI: SHRIMP U-Pb Dating on the Coesite-Bearing Zircons From Gneissic Cores in the Main Drill Hole of Chinese Continental Scientific Drilling Project (CCSD-MH), SW Sulu terrane
AU: * Liu, F
EM: liufulai@ccsd.cn
AF: Institute of Geology, Chinese Academy of Geological Sciences, No.26 Baiwanzhuang Road, Beijing 100037 China, Beijing, 100037 China
AU: Xu, Z
EM: xzq@ccsd.cn
AF: Institute of Geology, Chinese Academy of Geological Sciences, No.26 Baiwanzhuang Road, Beijing 100037 China, Beijing, 100037 China
AU: Xue, H
EM: huaiminxue@sina.com
AF: Institute of Geology, Chinese Academy of Geological Sciences, No.26 Baiwanzhuang Road, Beijing 100037 China, Beijing, 100037 China
AU: Liou, J
EM: liou@pangea.Stanford.edu
AF: Department of Geological and Environmental Sciences, Stanford University, Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305, USA, Stanford, CA 94305 United States
AB: Laser Raman spectroscopy and cathodoluminescence (CL) images show that most zircon separated from paragneiss in the main drill hole of Chinese Continental Scientific Drilling Project (CCSD-MH) at Maobei, southwestern Sulu terrane, retain low-P mineral-bearing detrital cores, coesite-bearing mantles and low-P mineral-bearing (e. g. quartz) or mineral inclusion-free rims. Sensitive High Resolution Ion Micro-probe (SHRIMP) U-Pb dating on these zoned zircons identified three discrete and meaningful age groups. Detrital zircon ages ranging from 659 to 313 Ma are recorded in the inherited cores, indicating the protolith age for the analyzed paragneiss is Paleozoic rather than Proterozoic. The UHP metamorphic event in the coesite-bearing mantles occurred at 228 ± 5 Ma, and the late amphibolite-facies retrogressive overprint in the outmost rims was at 213 ± 6 Ma. Combined with previous SHRIMP U-Pb dating results from orthogneiss in CCSD-MH (Liu et al., 2004), it is suggested that both Neoproterozoic granitic protolith and Paleozoic sedimentary rocks were subducted to mantle depths in Late Triassic (228 ± 5 Ma). About 15 million years later, the Sulu UHP metamorphic rocks were exhumed to mid-crustal levels and overprinted by an amphibolite-facies retrogressive metamorphism. The exhumation rate deduced from the SHRIMP data and metamorphic P-T conditions is about 6.7 km/Ma. Such a fast exhumation rate suggests that the Sulu UHP paragneiss and orthogneiss returned towards to the surface as dominant part of a buoyant sliver, caused as a consequence of slab breakoff.
DE: 3600 MINERALOGY AND PETROLOGY
DE: 3654 Ultra-high pressure metamorphism
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005