Geology and geochemistry of lava types in Lembang, West Java, Indonesia

This research study is conducted in Lembang, West Java, Indonesia. West Java is a part of Java Island which is believed to locate in the transitional zone between oblique subduction in Sumatra and orthogonal subduction at the eastern part of West Java that contribute to the series of volcanism in West Java. At least four volcanic complexes present at the West Java includes Galunggung-Tangkuban Parahu complex. The lithology of the study area is composed of the eruption products of Mount Tangkuban Parahu and its surrounding volcanoes. Mount Tangkuban Parahu is located within Sunda caldera, which is formed from the catastrophic phenomena, the collapsed of the summit of the giant Sunda volcano. The collapsed of the giant Sunda caldera caused the formation of major fault in the West Java known as Lembang fault with the total extends of 29 km. The research area had covered a part of Lembang fault which lies from East to West direction. This volcano-tectonic activity caused the geomorphological changes in the regional scale. Geological mapping is conducted by covering the area about 25 km2 in Lembang in order to produce the detail geological map and lava study of the research area. Lithology, geomorphology, stratigraphy and structural geology of the study area are been observed and recorded. The raw data of geological mapping is analysed using ArcGIS software and rose diagram software for the geological part. The study area consists of andesite of the Lembang fault scarp, the older volcanic breccia, basaltic lava, young volcanic breccia and tuff units. For the specification part, the five rocks samples are been collected which indicate two types of lava found in the study area, basaltic lava and andesite lava. These five samples are analysed using XRF analysis and been interpret by GCDkit 6.0 software. Based on the interpretation using TAS, Si02-K20 plot and Harker trends diagram, these two types of lava are represent a same magma suite which is talc-alkaline suite but different magma sources.