中国科学院地球化学研究所机构知识库

The late Permian-Triassic granites in southeastern China have important tectonic significance for the evolution of South China. Here, we present the detailed geochronological, geochemical and petrological analyses for the Jinlongyan (JLY) granite in northwest Fujian Province, southeast China. LA-ICP-MS zircon U-Pb dating yielded a weighted average ~(206)Pb/~(238)U age of 224.1 3.3 Ma. The granite is mainly comprised of K-feldspar, plagioclase, quartz, biotite and minor amphibole. It is characterized by enrichments in Rb, Th, REEs (total REE = 295.1-694.3 ppm), and HFSEs (e.g., Zr = 289- 520 ppm, Hf = 9.3-15.0 ppm, Y = 36.2-68.2 ppm) but depletions in Ba, Sr, Eu and Ti. The granite is metaluminous to weakly peraluminous and show a clear A-type granite geochemical signature with high SiO_2 (70.89 wt%- 75.76 wt%), total alkalis (Na_2O + K_2O = 7.51 wt% -8.72 wt%), Ga/Al ratios (10000 Ga/Al = 2.72-3.43). Insitu zircon Hf isotope analysis shows their epsilon_(Hf)(t) values ranging from -7.2 to -3.2, with Mesoproterozoic T_(2DM) ages (1308-1525 Ma). Whole-rock Nd isotope data show their epsilon_(Nd)(t) values in the range of -9.5 to -9.1 and yield paleoproterozoic T_(DM) ages (1606-1985 Ma). These characteristics indicate that the JLY A-type granite magma was formed by the partial melting of Meso-Paleoproterozoic crust rocks in the Cathaysia Block. Our study of the JLY A-type granite, together with other Triassic A-type granites in South China, defines an extensional environment in the late Triassic which probably was caused by the collision of the South China Block with Indochina Block.