The effect of collision of the Banggai-Sula microcontinent to the tectonic development in Central Indonesian region

Abstract

The geology of Indonesia is well-known as one of the most complex in the world, especially in the boundary between Eastern and Western Indonesia which is called Central Indonesia where geologically it is situated in the triple junction of the three major plates; Indo-Australian, Eurasian and Pacific plates. Considerable hypothesis have been put forward to explain its tectonic history but it still becomes subject to controversy. Makassar Strait, Sulawesi and Bone Bay are three major tectonic provinces situated in Central Indonesia which show very complex geology and tectonics. Several major faults existing in the region such as, Paternoster and Sangkulirang faults in Makassar Strait and Palu-Koro, Matano and WaIanae faults in Sulawesi as well as normal faults in Bone Bay are believed to be related to one another in their formation and control the tectonic development of the region. Geological and geophysical data in the region have been analysed to reveal the shallow and deep structure of the region. Seismic interpretation shows the presence of major faults indicating as extensional, compressional and inversion tectonics in Makassar Strait, Sulawesi and Bone Bay. While gravity models indicate the presence of oceanic crust in the middle of Makassar Strait and Bone Bay, as well as the presence of remnant subduction to the south of Bone Bay. The origin of oceanic crusts in · Makassar Strait an.d Bone Bay are interpreted as due to the rifting process forming rift structure as half­ graben. The driving mechanism of the rifting in Makassar Strait is suggested as a result of subduction roll-back ofthe Pacific Plate eastward since early Tertiary. Whereas the driving mechanism of the rifting in Bone Bay is due to the collision of Banggai-Sula Microcontinent to Sulawesi causing the displacement and rotation of two major faults, WaIanae and Palu-Koro faults, and finally caused the opening of Bone Bay. However; the effect of the collision is not only causing the opening of Bone Bay but also effecting the tectonic development in Central Indonesia. This is interpreted on the basis of the orientation, pattern and timing of many major faults in Central Indonesia which is in agreement to the extrusion model of Tapponnier et al. (1982). The model has been used to explain the tectonic settings in Southeast Asia in relation to the indentation of India continent to Eurasia. The result of this study also pres!lnts the tectonic model explaining the sequences of the tectonic evolution in Central Indonesia during the collision.