PETROGENESIS OF PRE-TERTIARY GRANITOID IN JAMBI AREA AND ITS IMPLICATIONS OF RARE EARTH ELEMENT ABUNDANCE

• Main Author: Najili, Ahmad
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/52992
• Institution: Institut Teknologi Bandung

Granitoid rocks are one of the main sources of the rare earth element (REE). Therefore, granitoid characterization becomes important in the early stages of REE exploration. Almost all granitoids in Indonesia have been mapped. However, detailed granitoid studies in Indonesia are still focusing on Bangka and Belitung Granite (tin belt granite). In contrast to Bangka and Belitung Granites, studies related to petrogenesis and granite characteristics on the mainland of Sumatra are rarely done, for example in the Jambi area. The aim of this study is to determine the characteristics of the Pre-Tertiary granitoids located in the Tigapuluh and Duabelas Mountains, Jambi. Granitoid characteristics include petrological and geochemical aspects. This study also focus on the petrogenesis of the Pre-Tertiary granitoid and its implications for the abundance of REEs. Megascopic and petrographic observations as well as geochemical analysis were done in this study. The Tanjungjabung Barat granitoids represent the Tigapuluh Mountains area, while the Sarolangun granitoids represent the Duabelas Mountains area. These two granitoids are Triassic to Jurassic in age. Based on megascopic and petrographic observations, both granitoids are classified as granite. Geochemical analysis shows that these two granitoids are A-type granite, which were formed in the postcollision environment, and derived from the crustal melting with ferrous alkalic to alkali-calcic peraluminous affinities. This crustal melting was caused by the collision of the Sibumasu Block with Indochina, resulting in crustal thickening and melting. The magma was contaminated effectively in the rift environment due to the subduction roll-back of the Meso-Tethys in the Late Triassic. Subduction in the West Sumatra also play some roles in the genesis, which is shown by the geochemical character of the Sarolangun granitoid. Effective contamination forms the characteristics of A-type granite that is rich in REE. The abundance of REE is indicated by the presence of alanite, monazite, apatite, zircon, and titanite. The author hopes that this study could improve the understanding of tectonic in Sumatra and the REE exploration in the area.