ROCK MAGNETIC AND PETROGENESA STUDIES TO IDENTIFY THE MAGMATISM PROCESS AND MAGMA PLUMBING SYSTEM BENEATH IJEN CRATER, BANYUWANGI, EAST JAVA

• Main Author: Pratama, Aditya
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/44299
• Institution: Institut Teknologi Bandung

Ijen Volcanic Complex which is located in Banyuwangi District, East Java, Indonesia, consisting of a large caldera with an area of 252 km2, in which there are more than 15 eruption centers. Among these eruption centers, Ijen Crater is the only one which is still active. Sulphure gases go out of the Ijen Crater every day and cause its lake water as one of the most acid in the world. Based on these facts, the study of magmatism process and magma plumbing system beneath the Ijen Crater becomes very interesting to be understood. In addition, this research will be focused to see the role of rock magnetism in the identification of magmatism process and magma plumbing system will be known. The samples used were lava taken from 13 different locations and included in the Ijen Crater eruption product in before 2,590 years ago. Geochemical measurements and rock magnetism characteristics were performed to each sample to determine the whole rock geochemistry, mineral geochemistry, magnetic susceptibility, remanent magnetization, Curie temperature and hysteresis parameters. The results of the Cpx-Opx Thermobarometry calculation showed that there are three magma storage zones beneath Ijen Crater, on the bottom of the crust (25-28 km), the middle of the crust (13-19 km), and the top of the crust ( ?10 km). Meanwhile, the magmatism process occurred before the eruption of Ijen Crater before 2,590 years ago was also quite complex. The process included magma crystallization, dissolution of plagioclase minerals, magma mixing, dynamic processes in the magma storage due to convection currents, exsolution process of titanomagnetite, degassing, and decompression processes. These results were obtained through analysis of rock and mineral textures, geochemical data, as well as magnetic mineral characteristics and rock magnetization parameters. Analysis of types of magnetic mineral can help identifying magmatism process, while through susceptibility analysis, it can be estimated the relative depth of the crystallization process and the magma cooling rate.