Collision of Micro-continents with Eastern Sulawesi: Records from Uplifted Reef Terraces and Proven-Potential Petroleum Plays

Proceedings, Indonesian Petroleum Association
Thirty-Fifth Annual Convention & Exhibition, May 2011

Collision of Micro-continents with Eastern Sulawesi: Records from Uplifted Reef Terraces and Proven-Potential Petroleum Plays

Awang Harun Satyana*, Margaretha E.M. Purwaningsih**
* BPMIGAS
** ConocoPhillips Indonesia

Abstract
Sulawesi is an assemblage of collided terranes. Australoid terranes comprising Buton-Tukang Besi and Banggai-Sula micro-continents collided with Eastern Sulawesi in the Neogene. Buton-Tukang Besi micro-continent collided with the SE Arm of Sulawesi/Muna Block from early Miocene until late Miocene. The collision has overthrusted the Kapantoreh ophiolitic suture, shortened and uplifted Buton. Tukang Besi, contrary to previous interpretations, is interpreted here as one micro-continent with Buton; which never collided with Buton. It separated from Buton as a response to post-collisional tectonics. Banggai-Sula micro-continent collided with the East Arm of Sulawesi beginning in the middle Miocene until Pliocene. The collision has overthrusted the East Sulawesi Ophiolite Belt, shortened and uplifted the frontal part of Banggai-Sula micro-continent.

Before the collision, the oceanic front of both micro-continents subducted beneath Eastern Sulawesi. Subduction ceased with the advent of collision. The junction between subducted oceanic crust and frontal micro-continents broke off and these continental parts began to exhume by gravity tectonics, causing collisional uplifts. We have observed coastal areas and islands sitting on these exhumed micro-continents comprising Buton, Wakatobi (Tukang Besi), and Luwuk (Banggai) areas. The uplifting of Quaternary reef terraces in these areas are manifestations of the collisional exhumation of the micro-continents. The rates of uplift range from 0.53 to 1.84 mm/year.

Foreland basins formed by collision are prolific hydrocarbon basins worldwide. Buton and Banggai Basins are proven petroleum provinces in Sulawesi. Collisional tectonics has affected formation of the foreland basins with structural traps, maturation of source rocks, and petroleum charging history. Several oil and gas fields are being produced in Banggai area. There is a significant asphalt mine in Buton and numerous oil and gas seeps have been recorded. The two basins are continually explored.

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