Geochemistry, petrogenesis and tectonic significance of the late Triassic A-type granite in Fujian, South China

Abstract

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 206Pb/238U 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 SiO2 (70.89 wt%–75.76 wt%), total alkalis (Na2O + K2O = 7.51 wt% –8.72 wt%), Ga/Al ratios (10000 Ga/Al = 2.72–3.43). In-situ zircon Hf isotope analysis shows their eHf(t) values ranging from −7.2 to −3.2, with Mesoproterozoic T2DM ages (1308–1525 Ma). Whole-rock Nd isotope data show their eNd(t) values in the range of −9.5 to −9.1 and yield paleoproterozoic TDM 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.