Petrology, Geochemistry and K-Ar Dating of Metamorphic Rock in Ciletuh Mélange Complex, West Java Indonesia

Abstract

The Ciletuh Mélange Complex in West Java, Indonesia, provides evidence of early Cenozoic subduction. This study aims to investigate the stratigraphic position, geological structure, metamorphic facies, and protoliths of the metamorphic rock units. The research methods employed geological mapping, petrology, and geochemical analysis. The samples collected exhibit different facies, including zeolites, greenschist, and epidote amphibolite. Protoliths consist of metasedimentary rocks such as metapellites, metapsammitics, meta-calcilates, and ortho-metamorphs such as metagabbro and metabasalt. Retrograde metamorphism, indicated by epidote, chlorite, and calcite in amphibolite schists, suggests lower temperature stress conditions. Hydrothermal changes are evidenced by some samples’ occurrence of quartz and calcite veins. Geochemical analysis reveals that the provenance of metasedimentary rocks originated from a volcanic arc, while the metabasalt rock originated from an island arc tectonic environment. K-Ar dating indicates an age range of 55.2 - 37.8 million years ago, corresponding to the Early to Late Eocene. These metamorphic rocks are believed to have formed through regional metamorphism due to island arc subduction and the formation of accretionary prisms. Retrograde metamorphism signifies uplift or accretion processes after tectonic activity.