STUDY OF PETROLOGY, MINERALOGY, AND GEOCHEMISTRY OF VOLCANIC ROCKS IN THE MOUNT SUNDA-TANGKUBAN PERAHU COMPLEX, WEST JAWA

• Main Author: Fadelia Hasan, Kurnaemi
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/72643
• Institution: Institut Teknologi Bandung

The Mount Sunda-Tangkuban Perahu complex consists of Mount Pra Sunda, Mount Sunda, Bukittunggul-Manglayang Complex, and Mount Tangkuban Perahu, which is still active today. This complex is in West Java Province, located close to Bandung City, which has a high population density. Therefore, understanding the characteristics of volcanoes is very important, one of which is helping to overcome future threatening disasters. This study aims to identify the petrological, mineralogical, and geochemical characteristics of volcanic rocks, determine the characteristics of the magma, and the history of magmatic evolution in the study area. The primary data used are 21 rock samples for petrographic analysis, six lava samples for mineral chemical data from the SEM-EDS test results, and secondary data obtained from 45 lava samples (XRF on 41 lava samples and XRF and ICP-MS on four lava samples), Digital Elevation Model (DEM), and also geological maps. The Mount Sunda-Tangkuban Perahu complex has three eruption periods, namely the pre-560 Ka period (Pre Sunda), the 560–180 Ka period (Mount Sunda), the 180–50 Ka period (Post Sunda or Mount Tangkuban Perahu). The pre-560 Ka period (Pra Sunda) has eruption products as andesite with SiO2 56–61 wt%. This rock has a porphyritic texture, phenocrysts in the form of plagioclase minerals with An43–68 (andesine–labradorite), augite, enstatite, olivine (Fo81–90), and magnetite; in a groundmass consisting of volcanic glass, plagioclase microlite, pyroxene, and fine crystalline opaque minerals. The 560–180 Ka period (Sunda Volcano) has an eruption product of basalt–andesite with SiO2 50–60 wt%. At the beginning of this period, the rocks had phenocrysts in the form of plagioclase An41–74 (andesine–bytownite), augite, and magnetite; in volcanic glass, plagioclase microlite, pyroxene, and fine crystalline opaque minerals groundmass. Whereas in the late period, the rocks have phenocrysts in the form of plagioclase An45–87 (andesine–bytownite), augite, enstatite, magnetite, and olivine (Fo76–89), in volcanic glass, plagioclase microlites, fine crystals of opaque minerals, pyroxene, and olivine groundmass. The 180–50 Ka period (Post Sunda or Mount Tangkuban Perahu) has eruption products in basaltic andesitic–trachyandesite rocks with SiO2 content of 54–57.5 wt%. In the early period, the rocks have phenocrysts as plagioclase minerals with An50–77 (andesine–bytownite), augite, and magnetite; in a groundmass consisting of volcanic glass, plagioclase microlite, fine crystalline opaque minerals, and pyroxene. Furthermore, in the late period, it has an eruption product of trachyandesite with SiO2 57–58 wt%. This rock has a phenocryst in the form of plagioclase minerals with An40–86 (andesine–bytownite), augite, magnetite, and olivine (Fo39–61), in a groundmass consisting of volcanic glass, plagioclase microlite, fine crystalline opaque minerals, pyroxene, and olivine. The volcanic activity of the Mount Sunda-Tangkuban Perahu complex has magma with tholeiitic and calc-alkaline affinities. The history of the Mount Sunda-Tangkuban Perahu Complex begins with the development of the Mount Pre-Sunda with magma that has undergone differentiation in the pre-560 Ka period, and this mountain produced eruption products in the form of lava units and pyroclastic flows. The formation of the Pre-Sunda Caldera also occurred in this period. In the initial period of 560–180 Ka, Mount Sunda developed and experienced volcanic activity, which produced eruption products in the form of lava units and pyroclastic flows with ongoing magma differentiation processes. The powerful eruption that occurred in this period also formed the Sunda Caldera. Furthermore, in the final period of 560–180 Ka, Mount Sunda experienced basaltic magma injection into previously differentiated magma, causing magma mixing. Eruptions at the Bukit Tunggul and Panenjoan Lava Cones also occurred. Mount Tangkuban Perahu developed in the early period 180–50 Ka. Magma activity in this period is still experiencing differentiation. In the late 180–50 Ka period, magma undergoes differentiation in crystal fractionation with eruption products in lava and pyroclastic. In addition, several basaltic magma injections may have occurred during this period.