QUANTITATIVE GEOCHEMISTRY APPLICATION FOR MAGMATISM PROCESS BASED ON KRAKATAU VOLCANO ERUPTION PRODUCT DATA USING PETROGRAM

• Main Author: Ardhya Wirananggapati, Muhammad
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/54454
• Institution: Institut Teknologi Bandung

Krakatau Volcano is one of active volcanoes located in Sunda Strait, Indonesia. The Krakatau Volcano Complex consists of Rakata, Sertung, Panjang and Anak Krakatau Island. This final project research objective is to analyze magmatism process based on geochemistry data from Krakatau Volcano eruption product using a Microsoft Excel-based petrology program, named PetroGram, which capable to perform either forward or inverse calculational approaches to the magmatism process. Magmatism processes that will be analyzed consists of characterization of geochemistry variations, mantle initial source, partial melting, and Assimilation-Fractional Crystallization (AFC). The major elements variations data trends from Anak Krakatau basaltic andesite and 1883 eruption rhyodacite shows a negative correlation between SiO2 against CaO, MgO, Al2O3, and a positive trend in SiO2 against Na2O + K2O, while in the trace elements, it has negative Eu anomaly, with LREE value was relatively decreased compared to MREE, with the MREE being not fractionated. There is a depleted Nb value, an enriched Pb value, enrcihed LILE (K, Rb, and Ba), and depleted HFSE (Nb, Ta, and Ti). Then, it can be seen that the increase in Cs, Rb, Ba, K, and Pb (LILE) values as well as the values of Th, U, Nb, and Zr (HFSE). However, there was a decrease in the values of Sr, P and Ti. Isotope variations data shows that the trend is moving to a more radiogenic direction. The Eu content in the magma source is more enriched compared to other Krakatau Volcano lava rock samples (positive anomaly), with the incompatible elements being slightly enriched compared to compatible elements. Mantle source partial melting occured above the garnetspinel lherzolite transition zone, with carbonate and quartzo-feldspathic sedimentary rocks possibly act as its contaminants.