Deepwater fold-thrust belt contraction driven by mixed deformation components

Abstract

The formation of fold-thrust belts is driven by compressive stresses caused by crustal tectonics, gravity, or a combination of both. The formation mechanism of a single compressive stress component has been thoroughly investigated by laboratory experiments and field observations. It is yet less well established how fold-thrust systems deform under multiple compressional stresses. The formation of the deepwater fold-thrust belt on the northwest Borneo margin has been previously explained by compressive gravity-driven stresses in the south and crustal-driven tectonics in the north. This study focuses on the transition zone between the gravity-driven south and crustal-driven north, and investigates the structural diversity around this transition using 3D seismic-reflection data. Structural interpretation results reveal two structural provinces distinct in deformation styles and structural kinematics within the deepwater fold-thrust belt. Folds and thrusts in each structural province reflect deformation stresses that occurred at different times with different orientation. Structural features in each structural province developed independently and were preserved largely without mixing in the fold-thrust belt, except for an interference zone of ca. 15 km in width. The fold-thrust belt can be interpreted to have formed by a multi-directional compressive stress system and exhibits greater structural heterogeneity than deformation caused by a single-component compressive stress system. Particular deformation characteristics and fault activity in the interference zone reflect a complex disparate compressive stress relationship.