Abstrak

The study of volcanoes in northwest Java has been largely overlooked. In this study, an investigation of the magma evolution and plumbing system of the Gede Salak volcano in the area was conducted. A geological survey determined the lava unit and volcanism. Whole-rock geochemistry is utilized to determine magma type and evolution. Mineral chemistry analysis revealed the magmatic process and phenocrysts` origin. Geothermobarometry is employed to estimate temperature and pressure. The volcanism comprised the eruption of lava flows, sector collapse, and the eruption of lava domes. The magma evolution consists of type A (lava flow and peripheral dome) and type B (summit dome). The processes identified are amphibole fractionation, magma mixing, and crust assimilation. Phenocryst textures and chemistry implied open-system processes in the plumbing system involving three magma series: the felsic, intermediate, and mafic. Magma type A resulted from multiple mafic recharges on the felsic series, while type B resulted from the mixing of intermediate and mafic series. The felsic and intermediate phenocryst crystallization occurred at 933–948°C and 1010–1011°C in the midcrust at 14 km to 17 km depth. Meanwhile, the mafic series reside in the lower crust at 21 km depth and 1065–1087°C temperature.