The Unique Tectonic Setting of

Sulawesi, Indonesia

Collison Between Salawesi and Kalimantan (Borneo)

Between the Miocene and the Early Pliocene the westward thrust along the Sorong transform fault system continued to transport Sulawesi towards Asia and into a collision with Kalimantan (Borneo). Evidence for this collision includes structural similarities in lineaments on both the east and west side of the Palu-Koro fault zone, and also close similarities between the Tertiary sedimentary rocks of eastern Kalimantan and the western arc of Sulawesi. Additionally, a Cretaceous melange, composed of rocks from the Merates Mountains, which is now a part of the southern arm of Sulawesi.

This movement eventually closed the ancient Sulawesi Sea and created the Makassar Straight which remained closed until the end of the Pliocene. This collision did not cause the volcanism and plutonic intrusions that might have been expected, although it did cause deformation of Kalimantan's Merates Mountains. A probably reason for the lack of volcanism is that rather than a normal subduction occuring, this collision probably resulted in an obduction. In the case of an obduction, part of the downgoing oceanic slab detaches along a preexisting discontinuity and is thrust onto the continental margin as an ophiolite.

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Collision between Kalimantan and Sulawesi, Miocene to the present. (Katali 1978)

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Map showing the Makasser Straight that developed following the closing of the ancient Sulawesi Sea (Katali 1978).

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