© IPA, 2006 - 6th Annual Convention Proceedings, 1977 PROCEEDINGS INDONESIAN PETROLEUM ASSOCIATION 317 Sixth AMWI Convention, May 1977 PAST AND PRESENT GEOTECTONIC POSITION OF SULAWESI, INDONESIA. JOHN A. KATILI *I ABSTRACT **) thrusts over them. The Strait of Makassar is Sulawesi with its peculair K-shaped pattern a marginal basin which was brought into is situated in an area where the Eur-Asian, existence by the spreading of the seafloor Indian-Australian and Pacific plates interact between Kalimantan and Sulawesi. and collide. The evolution of Sulawesi started in Mio- Complex geological processes in this area cene time or even earlier when 800 km east resulted in the transformation of a normal of Kalimantan a northsouth trending east island arc structure into an inverted one. facing island arc came into existence originating Deformation of an already tectonized belt, from a spreading center located in the sweeping of fragments against unrelated terrain, Pacific Ocean. thrusting of oceanic and mantle material over Collision between Sulawesi and the Aus- the island arc, closing of deepsea basins behind tralian-New Guinea plate which occurred in the ax, trapping of old oceanic crust caused early Pliocene time severely transformed by the bending of an island arc, formation of Sulawesi into an island with its convex side a marglnal basin by the spreading of the turned towards the coritiaent, at the same seafloor behind the arc, development of small time causing ibduction of opfriolite in the subduction zones with reverse polarities etc. eastern arc of this island. illustrate this phenomenon. The movement of the Pacific piate continued Small deepsea basins surrounding Sulawesi and gradually pushed Sulawesi towards the such as the Gulf of Bone and the Gulf of Asian continent resulting in the closing of Gorontalo originally formed the arc-trench the sea between Kalimantan and Sulawesi at gap of the Sulawesi island arc. the end of Pliocene. Collision took place, The Banda Sea is considered as an oceanic this time between tne western arc of Sulawesi crust trapped by the rolling up of the east- and eastern Kalimantan causing obduction of west trending Banda arc due to the north- ophiolites in the Meratus Mountains and slight ward drift of Australia combined with the deformation of the sediments in the eastern westward movement of the Pacific Plate. Kalimansan oil basins. Similarly the Sulawesi Sea consists of an old Opening of Makassar Strait took place in Pacific crust trapped by the westward bending Quaternary time along the Pasternoster and of the Sulawesi island arc caused by the Palu-Koro transform faults. spearheading westward thrust along the Sorong The first movement leading towards the transform fault system. Later a minor spreading opening of the strait began with a sinistral center became active in. the central part of transcurrent shift along the northwest-southeast the Sorong fault zone. The Molucca Sea trending Pasternoster fault, which affected comprises a tectonic melange situated between both Kalimantan and the sourhern part of the two colliding arcs of northern Sulawesi and the west arc of Sulawesi. Two small spreading western Halmahera. While the beaioff zones centers then developed, one each on the dip under the northern Sulawesi and Halma- northern and southern part of the Mabassar hera arcs in normal fashion, the melange Strait, connected by the Passernoster fault *) Director General of Minerals, Ministry of Mines, Jakarta, undoIresia) **) Abstract only is presented with illustrations. The full text will be published in Tecronophysks. , 318 which now acted as a dextral transform fault and moved the northern part 'of the western Sulawesi arc towards the east. Spreading in the southern part of the Makassar Strait was accomodated by an east- dipping small subduction zone which could be held responsible for the formation of the late Quaternary Lompobatamg and Barupu volcanoes in southern Sulawesi. In the northern part of the Makassar Strait the eastward movement of Sulawesi was checked by the newly formed Palu-Koro transform fault which moved the part of Sulawesi west of the fault in a south-south- easterly direction until the island gained its present position. This movement presumably caused destruction of the small spreading centers in the Makassar Strait and consequently terminated the activities of the late Quaternary volcanoes in southern Sulawesi. Some unsolved problems in relation to the geology of Sulawesi and the surrounding areas are also discussed. IAHERA K A LlM AN TAN 129" 130' w Y Figure 1 - Index map showing present geography of Sulawesi and surrounding islands v, 32c GEOLOGIC MAP OF SULAWESI-INDONESIA GEOLOGICkL SURVEY OF INDONESIA 1976 KM 120 122 124 126 Figure 2 - Geologic map of Sulawesi - Indonesia 32 I ac m 0 c I m 32 2 d 323 0' '00 0 3fl 0') 0 "30' 30' Figure 5 - Geology along the Palu-Koro fault zone - Central Sulawesi Y t 0 325 3 26 I m 327 Figure 9 - Hydrographic chart of Makassar Strait showing topographic scarps along Paster- noster and Palu-Koro fault zones. Figure 10 - Geology of the Meratus Meiintainc E: ier:. kalimantm \ 2- v) -4 V W- m b A MCP-5 I Q Figure 11 - East-West cross sections western margin of Makassar Strait Figure 12 - East-West cross sectibn northan portion of Kutei Basin HALMA SULI lRlAN.!dYA UEUA WtPi 332 miocene early Pliocene \ late Pliocene quaternary e) M LEGEND a Subduction zone Magmolic Ofc I( 4 LIMANTAN / Axis of spreading / Subduction zone / Tronrform ona tranacurrent fault .M Incipient plate boundaries present I 0 Active volcanoes Figure 14 - Diagrammatic portrayal of Miocene to Recent paleogeography of Sulawesi .