The structure and deformation history of the serpentinite bodies along the Bentong Suture: a case study at Bukit Rokan Barat

Along the boundary of the Western and the Central Belts of Peninsular Malaysia, there are a number of relatively small bodies of serpentinite outcrops. It is believed that these outcrops represent the serpentinised ultramafic rocks, which intruded the Lower Devonian rock formations. The serpentinite outcrop at Bukit Rokan Barat, Negeri Sembilan can be considered as one of the best that can be found in this area. The structure observed at this outcrop could represent the structure of the other serpentinite bodies situated along this boundary. Furthermore the deformation history, which is deduced from this structural study, may be used to describe the deformation history that took place along the boundary between the Western and Central Zones of Peninsular Malaysia. The observed serpentinite body at Bukit Rokan Barat is well foliated, trending approximately in north-northwest and northwest direction and moderately to steeply dipping towards northeast. This rock body had suffered at least three phases of shearing, the earlier two (D1 and D2), were related to ductile, while the third (D3) was related to brittle deformation. The ductile deformations are indicated by the presence of shear zones, foliations and crenulations folds (microfolds) and lenticular-shaped structures, and the brittle deformation by the lateral faults. The maximum principal paleo-stresses (sl) related to the ductile deformations (D1 and D2) were acting from NE and ENE directions respectively and the brittle deformation (D3) from NNE direction. The approximately EW tension cracks developed within the lenticular shaped structures are interpreted as the last phase of deformation suffered by this rock body