Ductile Deformation Rocks Along the Palu-Koro Fault Zone, Central Sulawesi, Indonesia

Abstract

The Palu-Koro fault is known as an active fault across metamorphic and plutonic rocks in the Central Sulawesi region. However, still difficult to find structural features and fault rocks along the fault line. Therefore, in this study, we have investigated the deformation characteristics  that have been experienced by the rocks that exposed along the fault zone. The microstructure analysis method has been applied through detailed petrographic observations to identifying deformation from quartz recrystallization and porphyroblast characteristics. Based on the quartz recrystallization data, almost the dynamic recrystallization are found in the Palu-Koro fault zone such as grain boundary migration, subgrain rotation and bulging, the bulging recrystallization with undulose extinction that demonstrated recovery with elongate parent and subgrain of the Miocene-Pliocene rocks of Kambuno granitoid in the western and southern sections of the fault zone. In contrast, there are not many high-temperature deformations and low strain rates such as grain boundary migration, although it is known that Kambuno granitoid rocks come into contact with other rocks in this area after metamorphism. The deformation of the rocks around the fault zone has occurred at least in two-stage. The first stage (D1) is still closely related to metamorphism marked by parallel schistosity in metamorphic rocks, recrystallization of grain boundary migration in Wana and Gumbasa Metamorphic complexes, and Kambuno plutonic rocks. The second stage (D2) is characterized by quartz bulging recrystallization and alignment of schistosity was overprinting by C’ shear band or S2 fold crenulation, inter-tectonic porphyroblasts. Both shear band  and porphyroblasts are indicated that the sinistral and dextral sense of shear, the sinistral porphyroblasts is consistent with the Palu-Koro movements whereas dextral sense is may be related to other tectonic movements before the rocks are in the position in the shear zone.