The geological evolution of Java Sea is marked by the movement of suduction zone from north to south direction. One of the subduction line is subduction and melang line is dissociating part of east and west of Indonesia ophiolite line in part of West Indonesia. The line start from part of west to east go out to sea through Karimunjawa High until Meratus Mountains in South Kalimantan. In Java, the ophiolite rock located in Ciletuh and Lok Ulo, while in Kalimantan in Meratus Mountain and Laut Island. The movement of subduction zone in Java Sea marked by difference age of basement rock in northern and southern of Java Sea. In northern shown by granite rock age in Belitung is 180 million years (early of Middle Jura), while in southern shown by the rocks around territorial waters of Bawean-Kangean Islands is 100,9 – 99.7 million years (Early – Late Cretacous), and more to southern around Peninsula Muria coast there are Muria Mt. is 1,1 – 0,4 million years and in Bawean Island on Java Sea as the volcanic rock with age 0,8 – 0,3 million years old (Late Pleistocene). Based on the line of structure and deepness of bedrock there are three tectonic periods in Java Sea, that is Extensional Rifting Paleogene – Early Miocene; compressional wrenching Neogen and compressional thrust-folding Plio-Pleistocene. While, based on stratigraphy and tectonic in Java Sea early by strain at basement rock (Paleosen – Early Miocene) which forming by graben followed by sedimentation process is the filling of the base of basin. The activity of strain desisted and followed by fold process at Middle – Late Miocene and Plio-Plistocene tectonic which predominated by volcanic sediment in shelf of Java Sea. Result of evolution that is formation the base of basinal at Pre-Tertiary (early Middle Yura – Late Creataceous) and Tertiary sediment at Paleocene – Early Miocene and high area at Pleistocene. Result of magnet analysis obtained by negative value of magnetic anomaly between -200 to -391,28 nT showing the basinal area and 100 to 338,89 nT as a high area. The high area on magnetic profile are Karimunjawa High in western and Bawean High in the eastern of the survey area. Bawean High as a boundary between Northeast Java Sea Basin and Pati Basin.
Keywords: evolution, basement rock, tectonic, magnetic, Java Sea, Pati Basin
Author : Ediar Usman, Ai Yuningsih