期刊
GONDWANA RESEARCH
卷 17, 期 4, 页码 615-631出版社
ELSEVIER
DOI: 10.1016/j.gr.2009.10.007
关键词
Charnockite; Petrology; Geochronology; Neo-Tethyan ridge subduction; Tibet
资金
- China Geological Survey Program [1212010918012]
- Chinese NSFC [40772049, 40972055]
- Foundation for Open Projects of State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences [GPMR200907]
The Gangdese batholith emplaced during the time span of Cretaceous to Neogene in the southern Lhasa terrane of Tibet has been considered as a major constituent of an Andean-type convergent margin derived from the northward subduction of the Neo-Tethyan oceanic lithosphere under Asia. Whereas previous studies assigned the Gangdese granitoids to be comprised predominantly of calc-alkaline rocks, here we report a suite of charnockites from the eastern part of the belt and characterize their petrology, geochemistry and age. These rocks possess an assemblage of andesine, enstatite, diopside, calcic amphibole, Ti-rich biotite, quartz and minor K-feldspar. Geochemically, they are characterized by intermediate SiO2 (54-63 wt.%). relatively high Al2O3 (15.9-18.9 wt.%), REE (55.7-89.4 ppm) and Sr (419.6-619.4 ppm), and low Y (11.3-17.2 ppm) and Yb (1.2-1.8 ppm) concentrations. The rocks display geochemical affinities similar to those of adakites derived from the partial melting of a subducted slab, and also can be compared to magnesian charnockites formed within a continental magmatic arc. The crystallization conditions of the charnockites were estimated at 900 degrees C and 1.0 GPa. LA-ICP-MS zircon U-Pb analyses of eleven samples yield consistent Pb-206/U-238 weighted mean ages of 86 to 90 Ma, indicating that the charnockites were emplaced in the Late Cretaceous. Considering the coeval calc-alkaline magmatism and high-temperature granulite-facies metamorphism, we propose that such high-temperature and low-H2O activity charnockites were derived through Neo-Tethyan mid-ocean ridge subduction before the collision of India with the Asian continent. (C) 2009 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
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