Fore-arc high and basin evolution offshore northern Sumatra using high-resolution marine geophysical datasets
Résumé
We present a morphotectonic study of the offshore northern Sumatra fore-arc high and fore-arc basin and an evolutionary model of the area based on high-resolution marine geophysical datasets. We show that the landward slope of the fore-arc high and the western edge of the Aceh fore-arc basin host a set of deeply-rooted, seaward-dipping backthrusts: main backthrust (MBT) and frontal backthrust (FBT), which we call north Sumatra backthrust system (NSBS). The FBT is imaged reaching the seafloor throughout the study area, whereas the MBT is imaged as a blind fault. Many landward-dipping imbricated thrusts (fore-arc high thrusts-FHT) are also observed below the fore-arc high, which along with the system of backthrusts have been responsible for uplifting the fore-arc high, shortening the Aceh Basin. On the landward slope of the fore-arc high, a strike-slip fault zone is imaged (termed West Andaman Fault - WAF - in accordance with previous studies), is readily interpreted as the product of the slip-partitioning at this oblique convergent margin, with a fraction of the arc-parallel slip localizing at the boundary between fore-arc high and fore-arc basin. Our results allow us to establish the evolutionary history of the thrust faults, strike-slip fault zone and the fore-arc basin. We suggest that the major structural features including backthrusts (MBT, FBT), fore-thrusts (FHTs) and the fore-arc high were developed during the Miocene, and that the growth of the fore-arc high accelerated in the Pliocene onwards owing to a sudden increase in sediment volume provided by the Nicobar fan.