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Geochronological, Geochemical Characteristics and Geological Significance of Tadong Granodiorite Pluton in the Western Section of West Qinling(PDF)


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Geochronological, Geochemical Characteristics and Geological Significance of Tadong Granodiorite Pluton in the Western Section of West Qinling
XU Duo-xun YANG Shuan-hai LI Rui-bao WANG Wei-feng WEI Li-yong LI Fei LIU Man-nian CHANG Liang LI Guo-ying LIU Xia
1. No.5 Gold Geological Party of Chinese People’s Armed Police Force, Xi’an 710100, Shaanxi, China; 2. School of Earth Science and Resources, Chang’an University, Xi’an 710054, Shaanxi, China
geochemistry granodiorite adakitic rock zircon U-Pb age petrogenesis tectonic post-collision West Qinling
Tadong granodiorite pluton, which is located in the western section of West Qinling orogenic belt, is mainly composed of gray-white fine-to-medium grained massive granodiorite without any dioritic enclaves, and several schist xenoliths are found at the margin of the pluton. LA-ICP-MS zircon U-Pb isotope chronology of the pluton was analyzed. The zircons have the characteristics of magmatic oscillatory zoning. The ratios of mass fractions of Th and U are mainly more than 0.4, and the U-Pb weighted average age of zircon is (219.0±5.3)Ma, which represents the crystallization age of Tadong granodiorite pluton. The geochemical characteristics show that the pluton has the characteristics of high-K calc-alkaline granite, including high mass fraction of SiO2 (66.88%-67.46%), high mass fraction of Al2O3 (15.39%-16.54%), K-rich (the mass fraction is 2.83%-4.12%) and metaluminous (the value of A/CNK is 0.97-1.0). Chondrite-normalized REE pattern of the pluton is right-inclined, which displays obvious differentiation of light and heavy rare earth elements and weak Eu anomaly. Primitive mantle-normalized trace element spider diagram of the pluton shows that large ion lithophile elements (Cs, Rb, Ba, etc.) are obviously enriched, heavy rare earth elements and high field strength elements (Nb, Ta, etc.) are depleted. The characteristics of Tadong granodiorite pluton are similar to adakite-like granite, which is typical of high mass fraction of Sr(mainly more than 400×10-6), low mass fraction of Y ((5.49-12.8)×10-6), low mass fraction of Yb ((0.34-0.91)×10-6) and high ratio of mass fractions between Sr and Y (more than 40, mostly 50-90). Petrogenesis results show that Tadong granodiorite pluton may result from the partly melt of garnet amphibolite (volume fraction of garnet is 10%-20%) from the thickening lower crust, following the process of fractionation and crystallization. In general, Paleotethys has closed at the later stage of Indosinian in the western section of West Qinling, and the syn-collision orogenesis between the north and south blocks finishes, following the tectonic evolution stage of post-collision.




Last Update: 2015-05-27