PETROLOGY AND MINERALOGY OF ANDESITE LAVA IN WAYANG WINDU MOUNTAIN COMPLEX, BANDUNG, WEST JAVA

• Main Author: ANARTA DRANISWARI (NIM: 22015032), WINDI
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/31644
• Institution: Institut Teknologi Bandung

Lithology composition, mineral chemistry characteristic and plagioclase microtexture of volcanic rock can represent magmatic process and magma evolution during volcanic rock formation. Meanwhile, magma formation temperature can be known based on the composition of co-existing pyroxene. This research applies petrographic analysis and mineral chemistry method on olivine, pyroxene, plagioclase, hornblende, opaque mineral, and quartz from andesite lava of Wayang Windu Mountain Complex that located in Bandung, West Java. Wayang Windu Mountain complex consist of 3 Khuluk; Khuluk Wayang, Khuluk Bedil, and Khuluk Windu. Lava product of Khuluk Wayang are pyroxene andesite and olivine bearing andesite, Khuluk Bedil is pyroxene andesite, and Khuluk Windu with lava products consist of pyroxene andesite and olivine bearing andesite. <br /> <br /> The andesite lava units of Wayang Windu Mountain Complex has a kalk-alkali affinity. The processes that occur in the magma chamber of Wayang Windu Mountain Complex include crystals fractionation, magma assimilation, magma mixing, new magma injection, dissolution followed by decomposition, and decompression. The magmatic evolution of Wayang Windu Mountain Complex begins with the formation of Wayang andesite-basaltic magma at 1100o C which involves the process of magma assimilation, crystal fractionation, and magma mixing. Wayang andesite-basaltic magma is strongly influenced by adiabatic decompression and convection when magma moves toward the surface and produces lava flows. Decreasing in temperature occurs in the magma chamber and produce Bedil andesite magma with temperature 900-1000o C. This process is followed by magma assimilation process, magma mixing, and fractionation of crystals. Magma chamber conditions are relatively stable when the eruption column move to north to form Bedil Lava Dome. Bedil Lava Dome eruption is strongly influenced by the sin-eruptive decompression process. Furthermore, intensive basaltic magma injection occurs in magma chamber followed by magma mixing, magma assimilation, and crystal fractionation resulting in Windu andesite-basaltic magma at 1100-1200o C. The magma chamber at that time was strongly influenced by adiabatic decompression and convection processes.