ZIRCON U-Pb GEOCHRONOLOGY, Hf ISOTOPE COMPOSITION, AND PETROCHEMICAL CHARACTERISTICS OF PALEOCENE GRANITOIDS IN THE WESTERN GANGDESE BELT, TIBET
J.Q. Lin1, F. Ding1,2, C.H. Chen1,2, T. Shen3
1College of Earth Sciences, Chengdu Sichuan, 610059, China
2Key Laboratory of Tectonic Controls on Mineralization and Hydrocarbon Accumulation, Ministry of Natural Resources, Chengdu University of Technology, Chengdu Sichuan, 610059, China
3403 Geological Brigade of Sichuan Bureau of Geology and Mineral Resources, Emei, 614200, China
Keywords: Zircon U-Pb dating, Hf isotope, Nuocang area, Gangdese Belt
Abstract
The research team studied the petrology, whole-rock geochemistry, zircon U-Pb age, and stable isotopic characteristics of the Rongguo Longba and Garongcuo granites of the Nuocang area to understand better the impact of Neo-Tethys ocean subduction and India-Eurasia continental collision on Paleocene tectonomagmatic processes along the southern margin of the Gangdese Belt. The Rongguo Longba granite and Garongcuo granite porphyry formed at 61.86 and 62.17 Ma, respectively. The Nuocang granitoids are characterized by (1) high SiO2, NaO2, and Al2O3 contents and low FeOtot, MgO, and TiO2 contents; (2) LREE and LILE enrichment and HREE and HFSE (Nb, P, and Ti) depletion; and (3) obvious negative Eu anomalies. These features indicate that the Nuocang granites are of the high-K calc-alkaline and peraluminous granite types. Furthermore, their zircon Hf isotope characteristics suggest that the magma source region has an ancient crystalline basement. The basaltic andesitic crystal tuff is the product of garnet-peridotite partial melting and crust contamination from rising magma emplacement.
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