Petrogenesis of volcanic rocks on Karimunjawa Islands, Central Java, Indonesia Mirzam Abdurrachman (a*), Radhitya Eka Pradipta (a), Wildan Nur Hamzah (a,b), Emmy Suparka (a)
a) Geological Engineering Study Program, Bandung Institute of Technology, Indonesia
*mirzam[at]gl.itb.ac.id
b) Akita University, Japan
Abstract
The Karimunjawa Islands (KI), Central Java, Indonesia is located at the southeastern margin of Sundaland. In this study we examined the petrology and geochemistry of volcanic rocks from Parang Island (PI) (6.5-5.6 Ma) and Genting Island (GI) (2.5-1.8 Ma). The link between Genting and Parang Islands with plate subduction is not simple since there are subduction^s angle changing along the Java Trench. The complexity might be related to the composition of overriding plate, the age of subducted plate and also by the presence of micro continent. This study aims to better understand the structure beneath KI and tectonic evolution of southeastern margin of Sundaland. The lavas from both Genting and Parang are basalt in composition with TiO2 ranges 1.51-2.65 % Wt, La/Yb > 7 and Nb/La>0.91. This condition implies a common magma genesis related to the upper mantle plume on non subduction setting. The presence of mantle upwelling in the upper mantle might be caused by the thinning of subducted slab beneath KI. New tectonic scenario in this area is presented.
Keywords: Petrology- Geochemistry- Karimunjawa Islands- Central Java- Indonesia
