THE COLLISION OF THE EAST JAVA MICROPLATE AND ITS IMPLICATION FOR HYDROCARBON OCCURRENCES IN THE EAST JAVA BASIN

摘要

The East Java basin is one of the major petroliferous basins in Indonesia. However, understanding of the tectonic development of the area is still subject to ongoing debate. Detailed regional geologic investigation was carried out to study and evaluate tectonic history and basin development in relation to hydrocarbon potential of the area. Recently acquired seismic data and hydrocarbon discovery in the sandstone unit of the Ngimbang Fm. in the EJ-1 well at East Java triggered a new interpretation of tectonism and basin development, especially during Paleogene time. From the end of Cretaceous to Early Eocene, a continental fragment, possibly detached from the Gondwana super-continent to the south, drifted northeastward approaching the Late Cretaceous to early Tertiary subduction complex (Lok Ulo-Meratus belt). The collision of this micro-continent with the eastern margin of the Sunda Microplate caused the Eocene magmatic activity to cease and uplifted the subduction complex, creating the Meratus Mountains in the eastern part of Kalimantan and The Lok Ulo melange complex in the central Java. The grain of the continental basement influenced basin trends. In eastern part of East Java Basin the dominant basement grain is E-W, as can be particularly well observed controlling the Kendeng and Madura Troughs. At the very close of this period, compressional tectonism due to the northward convergence between the Australian plate and the Sundaland margin reactivated these pre-existing E-W basement faults into strike-slip movement (e.g. along the Sakala Fault Zone). Another type of basin configuration developed at the collision zone oriented NE-SW, parallel to the direction of the collisional suture along Lok Ulo - Meratus Complexes. As a result, it is proposed that the Muria Trough in the north is a foreland basin which probably can be traced further south through Kendal Sub-basin to Kebumen Sub-basin. The result of this study reveals a new target for hydrocarbon exploration in the area.