Kinematics of the Mantano Fault, Sulawesi
Ian Watkinson and Robert Hall, completed project
This project aims to understand strike-slip faults in central and southeast Sulawesi, such as the Matano, Lawanopo and Mendoke faults, particularly how they relate to the Palu-Koro fault, and what part this system plays in the tectonic development of central Indonesia.
The Matano Fault trends about 200 km WNW from southern central Sulawesi, and is marked by a major, broadly linear valley, within which lies Lake Matano. The fault is typically shown to mark the southern edge of the Sula Block, linking to the Palu-Koro Fault to the west and the North Sulawesi Trench to the north (e.g. Hamilton 1979; Rangin et al. 1999). Such a hard linkage between either the Lawanopo or Matano and Palu Koro faults is a requirement of many rigid-block rotation models for Sulawesi (e.g. Bellier et al. 2006; Socquet et al. 2006). However, structural continuity between the faults is more complicated than this model indicates, and very few studies have been made of the Matano Fault to corroborate such ideas.
Reconnaissance fieldwork shows that the western end of the Matano fault is highly segmented, to within about 50 km of its apparent western termination, where a single strand curves close to the southern end of the Palu-Koro Fault. Many fault strands are lined by a thick smear of serpentinised peridotite, which may have been laterally translated from the East Sulawesi Ophiolite, and serves as a tectonic lubricant. Phyllonitic schist and metaconglomerate are locally exposed within the fault zone, mylonitic fabrics record strike-slip shear under ductile conditions. Rare pseudotachylites occur where the fault cuts crystalline rocks. Intact slivers of mudstone, marble, calc schist and amphibolite lie within fault strands, and bedding and foliation curve into parallelism with the fault. Kinematic indicators within the slivers show sinistral shear. Fault zones showing these features are several tens of metres wide, and enclose kilometre-scale lenticular mountains within their anastomosing network.