AMERICAN ASSOCIATION OF PETROLEUM GEOLOGISTS (AAPG) International Conference and Exhibition Perth, Australia, November 5-8, 2006 New Insight on Tectonics of Central Java, Indonesia and Its Petroleum Implications Awang Harun Satyana (BPMIGAS - Indonesia’s Executive Agency for Upstream Oil and Gas Business Activities ) EXTENDED ABSTRACT Central Java, in the middle part of the Java Island, Indonesia, shows a conspicuous re- entrants or indentation of its coastlines compared to those of western and eastern Java (Figure 1). This indentation is considered to express a wrench segmentation. Two major Paleogene strike-slip faults with opposing trends and slips are responsible for the indentation. The faults are called (1) the Muria- Kebumen Fault, left-lateral, trending southwest-northeast; and (2) the Pamanukan-Cilacap Fault, right-lateral, trending northwest-southeast. The two faults caused significant geologic changes in Central Java. The faults caused : indentations of northern and southern coastlines, subsidence of North Central Java, uplift of the Serayu Range and exposure of the pre-Tertiary Luk Ulo melange complex, disappearance of the Southern Mountains of Java in southern Central Java due to subsidence, and northward shifting of the Quaternary volcanic arc in Central Java. This new tectonic insight of Central Java gives reasoning why basins in Central Java are different with its counterparts in western and eastern Java and presenting where to look for possible petroleum possibilities in this area. Regional Tectonics and Structures of Java Island Java Island occupies an active margin of plate interaction between Eurasia continental plate and Indian oceanic plate, which have converged since Juro- Cretaceous. Therefore, the basement of Java Island is composed of both Eurasian continental crust (northern West Java and Central Java) and intermediate accreted terrane (southern West Java, southern Central Java and almost East Java). The presence of some micro-continents is also possible in Java, like in the Jampang and Bayat areas. The main tectonic elements resulted from the convergence include : subduction trenches, magmatic-volcanic arcs, accretionary prisms, and back-arc and fore-arc basins. Sedimentary and volcanoclastic rocks intruded by some magmatic intrusions cover the basement rocks. Central Java occupies a transition between dominantly continental basement at West Java and dominantly intermediate basement at East Java. Structural trends of Java Island can be grouped into four groups, including : (1) Meratus Trend (southwest-northeast), (2) Sunda Trend (north-south), (3) Java Trend (west-east), and (4) Sumatra Trend (northwest-southeast). The structures with Sumatra Trend mainly exist in West Java area and disappear to the east of Central Java area. Whereas, the structures of Meratus Trend dominate the structural grains of northern East Java and getting reducing and disappearing to the west of Central Java. It looks that Central Java