ANALOGUE MODELING OF RIFT MECHANISM IN THE PALEOGENE GRABEN SYSTEM OF WESTERN INDONESIA

摘要

Paleogene deformation of Western Indonesia is characterized by extensional fault systems forming a series of rift basins. The orientation of this Paleogene rift system varies from the west to the east. In general, two main orientations are recognized from seismic interpretation: north to south and northwest to south east trends. Some basins are dominated by a single extensional fault orientation and the others have more than one extensional fault system. However, the mechanism of their formation is not clear. In addition, all tectonic models of the SE Asia region conclude that Western Indonesia acted as a convergent margin during this period of time. This paper demonstrates the use of sandbox modeling in explaining the rift mechanism of the Paleogene fault system of Western Indonesia, specifically in the Central Sumatra Basin. Our sandbox modeling setting was developed based on structural interpretation and reconstruction of numerous seismic data particularly in the Central Sumatra Basin. We built a configuration of mosaic basement in the sandbox model that represents the Pre-Tertiary existing structures in Sumatra. The Mutus, Mergui, and Malacca terrain sutures are represented as the boundary of the basement block in sandbox model. These blocks are placed on a rigid plate which is then moved by dextral movements of the wall representing the dextral movement along the Great Sumatran Fault Zone and the Raub-Bentong Fault System. The result of the study indicates that the rift orientation of Paleogene system is highly controlled by pre-existing basement structures. Jigsaw type basement structures generate local troughs, with their orientation highly dependant on the main principle stress axis. The rift mechanism is mostly controlled by NW-SE trending right-lateral, strike-slip movement which suggests this fault system must have been developed prior to the extensional event. This conclusion is supported by evidence of basement high and low structures, such as Tiga Puluh Mountain and Bengkalis Trough, along a major regional suture.