HR: 1400h
AN: V53A-01    [Abstracts]
TI: Age and Petrogenesis of Garnet Peridotites in the Sulu Ultrahigh-Pressure Metamorphic Belt
AU: * Meng, Q
EM: mengq@muohio.edu
AF: Miami University, Dept. of Geology, 114 Shideler Hall, Oxford, OH 45056, United States
AU: Widom, E
EM: widome@muohio.edu
AF: Miami University, Dept. of Geology, 114 Shideler Hall, Oxford, OH 45056, United States
AU: Yang, J
EM: yangjsui@ccsd.org.cn
AF: Chinese Academy of Geological Sciences, Institute of Geology, 26 Baiwanzhuang Road, Beijing, 100037, China
AU: Chen, S
EM: njcshizhong@cgs.gov.cn
AF: Chinese Academy of Geological Sciences, Institute of Geology, 26 Baiwanzhuang Road, Beijing, 100037, China
AB: Investigations of garnet peridotites in the Dabie-Sulu ultrahigh-pressure (UHP) metamorphic belt indicate that they have experienced subduction zone UHP metamorphism and mantle metasomatism. However, the formation age, origin and source of the garnet peridotites are still poorly constrained. Re-Os formation ages of 1.8 and 2 Ga are obtained for Raobozhai peridotites from the Dabie terrane and Xugou peridotites from the Sulu terrane, respectively [1,2]. The latter is interpreted to originate from the Yangtze craton. Although the basement beneath the Yangtze craton and the continental lithospheric mantle (CLM) of the eastern block of the North China craton prior to Triassic was Archean, no Archean formation ages of peridotites have been reported from the Dabie-Sulu UHP metamorphic belt. We report Re-Os isotopic results for garnet peridotites from the Pre-pilot hole 1 (PP1) of the Chinese Continental Scientific Drilling Project, located in the western part of the Sulu terrane. Samples from 147 to 245 m include harzburgite, lherzolite, dunite and serpentinite. They are fresher and less serpentinized than those in any other drill holes or field outcrops. Os and Re concentrations range from 0.0089-3.7345 ppb and 0.0049-0.2489 ppb, respectively, with 187Re/188Os varying from 0.0067-6.9925 and 187Os/188Os varying from 0.11163-0.15723. The lack of correlation between 187Os/188Os and 187Re/188Os indicates that the Re-Os isotope system has been disturbed by later metasomatism due to Re mobility. However, most PP1 samples have unradiogenic 187Os/188Os varying from 0.11163-0.11730, among the most depleted peridotites found in China. Re depletion ages (TRD) range from 1.22 to 2.43 Ga, indicating that the PP1 peridotites are at least 2.43 Ga in age. Re-Os model ages (TMA) range from 0.095-2.881 Ga, and three samples have Archean TMA, indicating that the PP1 peridotites could have originated from refractory Archean CLM beneath either the North China or Yangtze cratons. References [1] Jin, Y. et al. 2004 Chinese Science Bulletin 49, 508-513 [2] Yuan, H. et al. 2007 Chemical Geology 236, 323-338
DE: 1025 Composition of the mantle
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 1038 Mantle processes (3621)
DE: 1040 Radiogenic isotope geochemistry
DE: 1115 Radioisotope geochronology
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly