Evolution of the West Baram Line Syntaxis, Borneo

Abstract

The West Baram Line syntaxis marks the boundary between the Sarawak collisional belt salient and the Sabah subduction-related recess and constitutes a major structural feature within the Rajang Group Fold-and-Thrust Belt in the central highlands of Sarawak State. Collision of the Luconia-Dangerous Grounds continental promontory terminated subduction of Proto-South China Sea oceanic crust beneath Southwest Borneo. Indentation of this allochthonous promontory created an asymmetric divergent salient and symmetrical doubly-convergent recess pair hosting isoclinally folded and thrusted members of the Rajang Group. The pre-deformational margin architecture controls the presence and geometry of salients and recesses within the fold-and-thrust belt. Apex convergence of structural trend-lines, rotation of nominally east-northeast structural trends to the north-northeast and a reduction in the length and morphology of folds eastwards supports indentor-controlled evolution of orogenic curvature. Evolution of the salient-recess pairs and orogenic curvature comprised complete and diachronous convergence of laterally heterogeneous crust. Convergence obliquity and laterally heterogeneous depth to decollement also affect the geometry of structures each side of the syntaxis. Structural interpretation of remotely sensed Landsat, SRTM and ASTER data illustrates the map-view geometry, dimensions and variation of fault and fold architecture that define the tectonic evolution of the Rajang Group Fold-and-Thrust belt in the region of the West Baram Line syntaxis. The Bandar Abbas syntaxis marks the boundary between the Zagros collisional belt and the Makran subduction-related prism and demonstrates a structurally analogous evolution due to an indenting continental promontory.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015