Bulletin of the Geological Society of Malaysia, Volume 69, May 2020, pp. 27 – 37

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

Ronaldo Irzon^1,2,*, Ildrem Syafri¹, Azman A. Ghani³, Arief Prabowo², Johannes Hutabarat¹, Purnama Sendjaja²

1 Faculty of Geological Engineering, Padjadjan University, Bandung, West Jawa, Indonesia, Indonesia
2 Center for Geological Survey, Geological Agency, Ministry of Energy and Mineral Resources, Indonesia
3 Department of Geology, University of Malaya, Kuala Lumpur 50603, Malaysia
* Corresponding author email address: ronaldoirzon18@gmail.com

Abstract: 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, Fe₂O_3T, 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.

Keywords: Pinkish granitoid, geochemistry, Lagoi, Peninsular Malaysia

DOI: https://doi.org/10.7186/bgsm69202003