Bulletin of the Geological Society of Malaysia, No. 66, December 2018, pp. 47 – 56
Aftab Alam Khan
Dhaka University, Plot 147, Road 2, Section 12A, Mirpur, Dhaka-1216, Bangladesh
Email address: email@example.com
Abstract: Evidences derived from petrotectonic assemblages strongly support that early crust of SW Borneo has evolved from depleted basaltic to enriched andesitic composition of intra-oceanic subduction melts. Tectonic model suggests that early crust of SW Borneo has undergone delamination and sinking through spontaneous instability due to rupture and resulting downwarping. Due to intrusion and lateral spreading of hot upper mantle, lower crust has undergone heating and partial melting resulted in the extrusion of primitive tholeiitic magma into the overlying basins. East-West trending Pre-Carboniferous inlier surrounded by Cretaceous intrusives and volcanics occurring in the Schwaner Mountains of SW Borneo mark the beginning of the collision episode in the Cretaceous. Occurrence of widespread oceanic rock assemblages, ophiolites, meta-sedimentary and igneous rocks in a NW-SE spatial zone signify derivation from paleo-ocean basin closure and evolved with suture zone, continental arc and an accretionary prism. Deformed Cretaceous flysch forming an accretionary complex occur as an extensive, dominantly Tertiary accretionary wedge to the north. Bouguer gravity response revealed a subduction trench and trench migration due to indentation of Luconia micro-continent on to the SW Borneo peri-continent edge after subduction had ceased. Tatau high in front of the Miri trench bear witness of an important collisional tectonics fed by igneous activities. Sibu high represents a segment of Luconia Block. Collision and subduction between Luconia micro-continent and SW Borneo peri-continent have evolved “Sarawak Suture” and “Continental Arc”.
Keywords: Early crust, petrotectonic assemblage, gravity anomaly, tectonic evolution, SW Borneo