Petrography and geochemistry of the Pinkish Lagoi Granite, Bintan Island: implication to magmatic differentiation, classification, and tectonic history

The combination of geochemistry and petrography analysis is useful in describing the source, evolution, type, and tectonic of granitoids. The closure of Palaeo-Tethys and the collision between Sibumasu and East Malaya are related to granitic magmatism in Southeast Asia which is classified into East Province, Main Range, and West Province with different characteristics. This study tries to characterize the magmatic differentiation, alphabetic classification, and tectonic history of Lagoi granite which is situated on the Eastern Granite Province in Southeast Asia based on the petrography and geochemistry analysis. Eight granitoid samples have been collected from Lagoi area and analyzed for both petrology and geochemistry using a polarized microscope, XRF, and ICP-MS. Petrographically, the granite consists of quartz, alkali feldspar, biotite, hornblende, and plagioclase. The pinkish Lagoi granite ranges from granodiorite to granite and shows metaluminous character. Seven of the samples are classified in high-K calc-alkaline series, whereas the other one is shoshonitic. The SiO2 content of high-K calc-alkaline group depicts very good negative correlation to TiO2, Al2O3, Fe2O3T, MnO, CaO, MgO, and P2O5 whilst positive one to K2O. Plagioclase reduction during magmatic differentiation is evidenced by Ba and Sr contents, Rb/Sr and CaO/Y ratios, and Eu negative anomaly. The rocks are categorized into I-type in relation to the location relative to Southeast Asia granitic belt, mineral content, and geochemistry composition. The pluton shows syn-collision affinity which formed at the time of Sibumasu and East Malaya collision