NEW PALEOMAGNETIC CONSTRAINTS ON THE CENOZOIC TECTONIC EVOLUTION OF THE NORTH ARM OF SULAWESI, INDONESIA

Extensive paleomagnetic sampling (34 sites) was carried out in Cenozoic formations of the North Arm of Sulawesi (between 120 and 124-degrees-E). Consistent results obtained between 120 and 122-degrees-E suggest the existence of a unique post-Miocene clockwise rotation of about 20-25-degrees of the western part of the North Arm. This rotation probably occurred during the northward drift of the North Arm along the Palu-Matano sinistral transcurrent fault. Between 122.5 and 124-degrees-E, both clockwise and counterclockwise rotations with various amplitudes (from +/-6-degrees to 85-degrees) are encountered, and these very likely correspond to individual microblock rotations due to pervasive deformation along shear zones. This result is consistent with the complex fault system of the Gorontalo and Kotamobagu shear zones that have been recognized on radar imagery and by SPOT image analyses.