PETROLOGY, MINERALOGY, AND GEOCHEMISTRY OF LAVA AT AGUNG VOLCANO, BALI: IMPLICATION FOR MAGMATIC PROCESSES AND EVOLUTION
Agung volcano is a stratovolcano located in Karangasem, Bali. The largest eruptions occurred in 1963 that caused thousands of casualties. The samples in this study are lava from the eruption before AD 1040 to AD 1963. The petrological, mineralogical and geochemical data are obtained from SEM-EDS, XR...
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| Format: | Theses |
| Language: | Indonesia |
| Online Access: | https://digilib.itb.ac.id/gdl/view/71645 |
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| Institution: | Institut Teknologi Bandung |
| Language: | Indonesia |
| Summary: | Agung volcano is a stratovolcano located in Karangasem, Bali. The largest eruptions occurred in 1963 that caused thousands of casualties. The samples in this study are lava from the eruption before AD 1040 to AD 1963. The petrological, mineralogical and geochemical data are obtained from SEM-EDS, XRF, and ICP-MS/OES. The obtained data are used to understand the characteristics of the magma, the magmatic processes and the temporal evolution of magma. There are three main groups: high aluminium basalt, medium potasium basaltic andesite and medium potasium andesite. All samples have porphyritic texture. The phenocrysts are plagioclase+augite+clinoenstatite+olivine+titanomagnetite±hornblende in the groundmass of plagioclase microlites, volcanic glass, titanomagnetite and pyroxene. Plagioclase, augite, clinoenstatite and olivine phenocrysts generally have normal zoning but magnesium or calcium content increase in the middle of the mineral. The dominant micro-textures are sieve texture, fine oscillatory zoning, glomerocrysts in plagioclase; pyroxene±symplectitic intergrowth of titanomagnetite reaction rims in olivine; and opacitic or augite+plagioclase+titanomagnetite reaction rims in hornblende. These micro-textures indicate open-system processes and disequilibrium conditions.
Agung volcano has calc-alkaline magma series with LILE and LREE enrichment in island arc situation. The magmatic evolution signs of changing composition from basalt to basaltic-andesite and andesite that are formed from the differentiation of the same parental magma. In addition, the magmatic process beneath the Agung volcano is dominated by crystal fractionation and repeated basaltic magma recharge. Furthermore, the comparative data of incompatible elements show the mantle composition modification due to the addition of carried sediment and oceanic crust fluid during the subduction process.
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