ABSTRACT

As an active margin, eastern margin of Sundaland had experienced various tectonic events throughout the Cenozoic and Quaternary. One implication of this tectonic activity was volcanism, so that volcanism itself directly reflects the tectonic setting. A correlation exists between geochemical and isotopic composition of magmas and the tectonic setting in which they were generated.

People tend to think that if there is volcanism then there is always subduction, because they see many examples of subduction-related volcanism. So, if there is a volcanic deposit, they will try to find where the subduction zone is. In fact, the tectonic setting that produces volcanic deposits can be various: constructive plate margins, destructive plate margins, oceanic intra- plate settings, continental intra-plate settings. Various tectonic settings had resulted in volcanic deposits and related magmatic intrusions in the eastern margin of Sundaland that can be found in the Makassar Strait and onshore South Arm of Sulawesi.

In these areas, Eocene Langi volcanics are found to be scattered in the Makassar Straits. Paleocene-early Miocene Langi, Bua, Salokalupang, and Kalamiseng volcanics are found in onshore South Sulawesi. Middle Miocene to Pliocene volcanics of Camba and Enrekang volcanics cover most of the onshore area of Sulawesi and include several volcanic depositional units. Up to the Pleistocene, South Sulawesi still showed its volcanism by Lompobatang and Barupu volcanism. Geochemical and isotopic data are available for these volcanic deposits, so that their petrotectonic settings can be known and they represent full suite of tectonism including: subduction, continental extension, and continental collision during the Cenozoic up to the Quaternary.

The petrotectonic settings of these volcanic deposits can examine the tectonic model applied for eastern margin of Sundaland because geochemical and isotopic characteristics of the volcanic deposits are distinctive of their tectonic settings. So, if one tectonic model is applied, but there is no evidence from its volcanic deposits then it can be said that the tectonic model is not correct.

The evolution of petrotectonic settings of volcanic deposits is used in this study to confirm the tectonic types of sedimentary basins that developed in the Makassar Strait, South Arm of Sulawesi, and Bone Bay. Also discussed what are the implications of these volcanisms for the elements and processes of the petroleum systems in these basins.