The Unique Tectonic Setting of

Sulawesi, Indonesia

The Rotating Plate Theory

It appears as though the northeastern section of the North Arm of Sulawesi is rotating in a clockwise direction past the East Arm and Kalimantan. On the southeastern side of the small plate is an arched system of left-lateral faults, while towards the north there is a zone of subduction at the North Sulawesi Trench as northeastern Sulawesi over rides the Celebes Sea Floor. At this trench the trend of northeastern Sulawesi changes from an easterly trend to a northerly direction. Active volcanism from the Sangihe Arc approaches this bend from the north, and a chain of extinct volcanoes extend westward from this bend. These extinict volcanoes, which have been have been inactive throughout Quaternary time, are thought to have originated from the Sangihe Benioff Zone.

A possible explaination for the right-handed bend in the North Arm is that the bend might be an orocline which has been progressing eastward. That would suggest that both the North Sulawesi Trench and the eastern trending segment of the North Arm have lengthened, while simultaneously the Sangihe Trench and the north-trending segment of the North Arm have shortened in a northern direction. The eastward progression of the oroclinal axis along the arm eventually caused subduction to the west of the axis to switch from westward below the eastern side to its current position, southward beneath the northern side of the arm.

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