Qing Hu, Nanjing Institute of Geology and Mineral Resources (China)
Qingtao Zeng, Nanjing Institute of Geology and Mineral Resources (China)
Jianren Mao, Nanjing Institute of Geology and Mineral Resources (China)
Haimin Ye, Nanjing Institute of Geology and Mineral Resources (China)
Xilin Zhao, Nanjing Institute of Geology and Mineral Resources (China)
Shangyou pluton is located in southwest China, approximately 3 km west of Shangyou county in Jiangxi Province. The pluton is in the east section of the tectonic-magmatic-mineralized zone of EW-striking Nanlin Mountain in Cathaysian Plate. Shangyou pluton trends in a NNE direction with an exposed area of 100km2.The pluton intrudes lower section in Cambrian strata in east and southeast sides, the west side is in contact with Devonian Tiaomajian Group sedimentary rocks. There is no contact metamorphism of Devonian strata in contact zone. Devonian strata are observed to overlap on the paleo-weathered crust of Shangyou pluton, and granitic clast-rich rocks formed at the base of the Devonian strata. The formation age of Shangyou pluton is judged to be late Caledonian by the contact relationship with the country strata, but now there are still lack of the exact isotopic age and systematic study for petrology and geochemistry.
SHRIMP zircon U-Pb age of Shangyou pluton is 464±11Ma. Strata of Tiaomajian Group in Middle Devonian overlap on the weathered crust of Shangyou pluton. Consistent geological characteristics and an isotopic age of the pluton indicate that the formation age is middle Ordovician during the Caledonian orogenic event. Ar-Ar plateau and inverse isochron ages of K-feldspar are 290.0±2.8 Ma and 289.7±5.4 Ma respectively. The biotite Ar-Ar total gas age is 295.5 Ma, implying that the Shangyou pluton recorded significant later thermal alteration events.
The Shangyou pluton is characterized by high Si, K and Al (averaging A/CNK, 1.11), corundum normative and rich in HREE, moderate negative anomaly Eu, rich in crust-derived high thermal elements, like K, Rb, U, Th. Basic high field strength elements (V, Cr, Co and Ni) are depleted, also depleted in Ti-Y, Nb-Ta, Zr, Sr, P and Ba. All of the data indicates that the Shangyou pluton belongs to the peraluminous crust-derived type granite with calc-alkaline series rock characteristics of active continental margin.
The (87Sr/86Sr) in ratio of Shangyou pluton is 0.707126∼0.712186, 147Sm/144Nd ratio of 0.1139∼0.1560, εnd(t) value of -7.29∼-10.22, (tDM) value 1.52∼1.63 Ga. These data are similar to those of Yashanian weakly peraluminous granites, and indicate crust mature degree in Paleozoic is lower than that in Mesozoic. The granite mainly resulted from the partial melting of continental crust meta-sedimentary rocks with low mature degree in Mid-Proterozoic, with some possible contributions of mantle-derived components.
A series of SE and NNE tensional-shear fractures occur at the folded center of basement in the study area due to inhomogenous convergence between continental plates after Yangtze Plate subducted into Cathaysian Plate, resulting in areas uplifting. Shangyou pluton is considered as post-collision granite, which was formed during the transition from a compression to tensional environment.