Gunung Beas Block, Ciletuh Region, District Ciemas, Sukabumi, located at 106 ° 23 ‘38.9 “- 106 ° 25’ 27.6” E Eand 7 ° 14 ‘27.6 “- 7 ° 12’ 46.2” S. This area has a unique geological feature where The pre-Tertiary rocks such as Ophiolites and Metamorphic Rocks is exposed. This study aimed to the wealth of geological data inventory in preparation for the development of “Geopark Ciletuh”.
The research methods used are study of literature, geological mapping, petrology, petrographic and geochemical analyzes. Then, the entire analysis is combined as a gudance in interpretation of petrotectonic environtment.
Based on the analysis of geomorphological and geological structure known that the area has experienced a complex geological structure and occurred in some tectonic periods. Regional stratigraphy in the area composed by pre-Tertiary rocks overlain uncoformably by Tertiary sedimentary rocks. Ophiolite rocks consisting of serpentinized peridotite, gabbro and amphibolized gabbro. Metamorphic rocks consisting of greenschist, phyllite and quartzite. Serpentinized peridotite indicates the condition of hydration of the peridotite thus serpentine minerals appears in the lower temperature and the pressure and affected by water. The presence of epidote, chlorite, and calcite in amphibolite showed retrograde metamorphism process in lower temperature-pressures condition. Quartz vein and calcite vein which occur in several sample showed hidrothermal alteration after the rocks is formed.
The tectonic environment of ophiolite genesis interpreted formed in Supra-subduction Zone (SSZ) or Island Arc, whereas metamorphic rocks formed by regional metamorphism during orogenic event.The retrograde metamorphism indicates the lifting or accretion process that occured by tectonic activity.
Keyword: Gunung Beas, Ciletuh, Petrology, Ophiolite, Metamorphic Rocks