Post-collision reactivation of the Bentong-Raub Suture Zone and regional tectonic implications

The Bentong-Raub Suture Zone (BRSZ) is one of the few remnants of the Paleo-Tethys Ocean, which completely closed in the late Triassic period. The main structural features of the BRSZ are expected to correspond to a compressional event during the Indosinian Orogeny. However, several studies in Peninsular Malaysia have suggested the reactivation of structures inherited from previous tectonic events during the late Mesozoic to Cenozoic times. In the present study, we conduct a regional structural analysis to investigate the deformation events affecting the BRSZ and report two new K-Ar ages of deformed igneous and metamorphic rocks. Three structural events have been identified along two transects (Lojing and Pos Betau) across the BRSZ: an initial ~E-W shortening (D1), followed by dextral shear in an N-S trend (D2), and a subsequent ~NW-SE extension (D3). Schistose granite and andesitic rock affected by the D2 event have been dated using the K-Ar method, yielding mid-Cretaceous ages. The D2 structures are commonly found on the steeply dipping bedding or foliation planes of the suture rocks, suggesting a structural reactivation of former orogenic D1 structures. Cross-cutting relationships and K-Ar ages suggest a D1 event corresponding to the Indosinian Orogeny’s compressional event, followed by a reactivation of its structures in the late Cretaceous as regional C-S fabric, where N-S dextral faults (D2) act as C-planes and NW-SE sinistral faults represent S-planes. Finally, a post-D2 relaxation period (D3) in a predominantly NW-SE extension direction is observed through the ubiquitous occurrence of normal movements, most likely linked to exhumation of adjacent granitic batholith, regional basin development and changes in the boundary conditions of the Sunda Plate during the Cenozoic.