Geology of Jelekong, West Java and the geochemical evolution of Waringin-Bedil Andesite

The petrology study is carried out at Jelekong, West Java, Indonesia to investigate the petrology of volcanic rocks under petrographic observation and the tectonic setting of the study area using geochemical analysis. A geological map of 1:25000 is produced. The study area covered 25 km2. Jelekong area consists of rocks produced from volcanic activity from Gunung Malabar Tua, Gunung Waringin, Gunung Bedil, Gunung Malabar and Gunung Tilu. The research area is made up volcanic rocks such as andesite, tuff and volcanic breccia. Based on historical geology, Jelekong is once a shallow marine environment before it is being deposited by volcanic rocks and materials during Pleistocene and become land environment. The land environment of Lake Deposits in the study area gone through erosion process which resulted in the present lake environment. The geochemical method used in this study is X-Ray Fluorescence (XRF) method, targeting major and trace elements. The elements are normalized to 100% and plotted to the related diagram. Major elements give information on the types of rocks when plotted on Peccerillo & Taylor (1976) diagram, the fractional crystallization of the andesite rocks when plotted on Harker diagram and also the tectonic settings and origin of magma. Trace elements help in determining the tectonic environment and tectonic settings when plotted on Spidergram diagram. The plotting diagrams show that Waringin-Bedil Andesite rocks are under calcalkaline which formed at subduction zone in the tectonic setting of Island Arc, with the depth of magma origin within ±114 km - ±127 km in Benioff zone.