GEOLOGI DAERAH HARGOWILIS DAN SEKITARNYA, KECAMATAN KOKAP, KABUPATEN KULON PROGO, DAERAH ISTIMEWA YOGYAKARTA

Abstract

Geographic Indonesia is located on a volcanic ring path, from the Tertiary era to the Resen volcanic arc stretching from Sumatra, Java to Banda. The Kulon Progo Mountains are part of the Oligocene-Miocene volcanic arc called old andesite. The research area is located in the area of Hargowilis and its surroundings, Kokap District, Kulon Progo Regency, Special Region of Yogyakarta. Research in the mountainous area of Kulon Progo was carried out because it is a complex of ancient volcanoes that have undergone intense morphological changes, rock deformation processes to form geological structures within a certain geological time. The research method used in this study includes the preliminary stage, the stage of observation and data collection, the stage of data collection and analysis consisting of structural analysis, petrographic analysis and micropaleontology analysis. The last stage is the preparation of a report based on the results of research and field data analysis. Geomorphology the research area consists of four geomorphic units, namely: Dam unit, volcanic upper slope hill unit, volcanic middle slope unit, and denudational hill unit with radial, rectangular and subdendritic flow patterns as well as mature to old area stadia. The stratigraphy in the study area is composed of four units sorted by old and young consisting of: the Kebo Butak andesite lava unit, the Kebo Butak andesite breccia unit, the Jonggrangan limestone unit, and the Sentolo calcarenite unit. The geological structure that develops in the study area is faults and joints with dominant directions northwest-southeast and north-south. The faults found in the study area include: Crangah normal fault, Mangun Plawangan left slip fault, Hargotirto left slip fault, Kalibuko left slip fault, Mount Reto left slip fault, Nganti left slip fault, Sermo Lor right slip fault, Hargorejo and Gawir normal faults volcano. Resources in the research area are lava mining and andesite breccia Kebo Butak, plantation land, agricultural land and water resources. Meanwhile, geological disasters that occur in the research area are in the form of rock mass movements. The geological history in the study area begins with the formation of the Kebo Butak Formation ranging from the Late Oligocene to Early Miocene. During the Middle Miocene-Pliocene, carbonate rocks began to develop in shallow-sloping seas. The ongoing subduction activity of the Indian Ocean under the Sunda Trench has caused the process of uplift of the Southern Mountains to date, in the study area marked by the death of carbonate sediment deposition and a change to the terrestrial environment. The process of structure formation is interpreted as having a north-south trend of compression, as well as erosion and weathering processes resulting in changes in the topography of Mount Ijo until it changes to what it is now.