TECTONOMAGMATISM STUDY IN KARIMUNJAWA ISLANDS

• Main Author: Eka Pradipta, Radhitya
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/43990
• Institution: Institut Teknologi Bandung

The Karimunjawa Islands are located in the north of Jepara City. At present tectonic setting in the Karimunjawa Islands which have volcanic rocks are back arc basin. The presence of deep seismicity under the Karimunjawa Islands is an anomaly. So the purpose of this study is to determine the formation process of Karimunjawa volcanic rocks and their implications for the tectonism of Java. The data consisted of field data and literature data (geochemistry of Muria Volcano, Lasem Volcano, Bawean Island, and seismic data). Geochemical data consists of main elements, trace elements, and rare earth elements. Seismic data were used to validate the tectonic model. Field appearance shows the columnar joint on Parang and Genting Island while in the middle of Genting Island there is a basalt boulder. Volcanic rocks on both islands have black color with porphiroaphanitic texture. Petrographic analysis results on both islands show trachytic texture with domination of plagioclase, pyroxene, and olivine as phenocrysts. The special texture found in the incision are sieve and iddingsite that is present surrounds mafic minerals. Whole rock geochemical analysis shows that the lithology of Parang and Genting Islands are basalt and trachybasalt with alkaline affinity to high potassium calc alkaline. The results of tectonic setting analysis showed that the location of the study area was an alkaline oceanic island. While the geochemical analysis on Muria Volcano, Lasem Volcano, and Bawean Island shows subduction related with tectonic setting is island arcs. The results of tectonic reconstruction in the past 20 million years have led to more gantle sloping angle in the oceanic plate which caused a shift in volcanism to the north. There oceanic plates are torned from Mount Muria to the south of the Karimunjawa Islands, which are marked by the seismicity in the area. The oceanic plate then returns as a deep earthquake in the middle of the Java Sea. In the study area, there are small tears under Parang and Genting Island which cause a upwelling of the mantle triggering volcanism in the Karimunjawa Islands.