Onshore record of the subduction of a crustal salient: example of the NW Borneo Wedge

Abstract : Subduction of oceanic highs has been described in offshore accretionary wedges thanks to bathymetric and seismic data, and simulated in sand-box models. Where documented, it is limited to oceanic subduction of small culminations (seamounts). However, tracing this phenomenon in ancient and/or uplifted belts remains a challenge. Based on structural, geomorphological and thermal analysis, we describe a subducted horst in the NW Borneo Wedge. This is evidenced by the occurrence of several geomorphological anomalies: a strong bend of the structural trend of the Rajang-Crocker Belt and an area with ′hummocky′ texture representing dismantled packages of sediments. Some specific structural features (large back and out-of-sequence thrusts in the internal zones, complex folds rooted on shear structures in the accretionary wedge) also occur in this central part of the NW Borneo Wedge. The central area of the related deformation zone records several thermal anomalies.