GEOLOGI DAERAH KEBONAGUNG DAN SEKITARNYA, KABUPATEN PACITAN, PROVINSI JAWA TIMUR

Abstract

The research area is located in Kebonagung and surronding, Pacitan Regency, East Java Province. The research area has a wide and varied distribution of igneous rocks and the presence of ore and alteration minerals. This research have a purpose to know geological condition of Kebonagung and surronding include geomorphology, stratigraphy, structure that affected to the exsisting of altered minerals and geological history. The method that used in this researchs such as field survey and analysis such as lineament analysis, structure analysis, petrography analysis, and microfossil analysis. The geomorphology of the research area consists of 4 units, namely the Volcanic Neck Hills Unit, the Lava Flow Hills Unit, the Karst Hills Unit, and the Alluvial Plains. The stratigraphic of the research area from old to young is obtained by sandstone units, andesite lava units 1, limestone units, dacitic lava units, and andesite lava units 2. The structure developed in the research area arestrike-slip fault that formed during the Early Miocene and Late Miocene with direction northeast-southwest that is strike-slip faul singgihan and strik-sip Fault Krajan In Late Oligocene the sandstone unit was deposited in land environments. In the beginning of Early Miocene, the volcanism produced the andesit lava unit 1 then in the same time the deformation occured and the first geological structure such as Strike Slip Fault Singgihan and minor fracture formed by the compression. The geological structure become the hidrothermal fluids pathway which is interpreted as unidentified residual of deep intrusion on the surface passed the side rock especially the andesit lava unit 1 and formed the alteration minerals. In the middle of Early Miocene, the limestone unit began to deposited in shallow marine environment. In the early of Late Miocene, the secondary deformation occured that involved the uplifting and volcanism then bring out the dacite unit as the product. Moreover, the deformation triggered the geological structure such as the Strike Slip Fault Krajan that crossed the limestone unit. The fault was the brecciation zone which created by the hydrothermal fluid as the residual of the freezing magma into the surface that passed the side rock such as the limestone and the alteration minerals occured. In the end of the Late Miocene, the volcanism still happened and the andesit lava unit 2 produced.