Morphotectonics of the Sumatra Margin -- Analysis of new Swath Bathymetry
Abstract
During several cruises with RV SONNE in 2005 and 2006 (SO186, SO189) systematic multibeam bathymetric surveys offshore Sumatra have been conducted. The bathymetric dataset now covers large parts of the trench and slope between Simeulue Island and the entrance to the Sunda strait. Here, we present a morphotectonic map and structural analysis of this new bathymetric dataset. The incoming oceanic crust, largely draped by a sedimentary cover, depicts a trench parallel conjugate, steeply dipping normal fault set building Horst and Graben structures. Two prominent ridges, the Investigator Ridge and the Wharton Ridge have a relief of 600 -700 m. In the vicinity to these ridges a second normal fault set has developed on the oceanic crust striking parallel to the ridges in N--S direction. These ridges as well as several other topographic highs further south are recently being subducted beneath the Sumatra margin. They deform and offset the lower slope and accretionary prism. The most prominent offset of about 15 km of the deformation front is observed in prolongation of the subducting Investigator Ridge. These ridges account for a general along strike segmentation of the deformation front and accretionary prism and possibly the subduction zone as a whole. The lower slope and accretionary prism are built up by a set of thrust faults and anticlines. In general fold axes strike NW -SE, parallel to the trench. However, where the ridges subduct beneath the slope, fold axes are rotated and strike NNW -SSE demonstrating a local rotation of the stress field. The recent activity of this domain is also expressed by an increased number of observed surficial collapse structures and slumps. Additionally, a third orientation of N--S striking lineaments is observed. These lineaments are especially pronounced by transverse channels and furrows feeding piggy back basins further up-slope. Along these lineaments fold axes are also offset, usually in a dextral sense. The structural inventory of the slope and accretionary prism thus depicts a complex interference of tectonic lineaments. This setting is partly due to the oblique convergence along the Sunda subduction zone with associated trench parallel and orthogonal strain partitioning, as well as the recent subduction of large oceanic ridges.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.U53A0033S
- Keywords:
-
- 3040 Plate tectonics (8150;
- 8155;
- 8157;
- 8158);
- 3045 Seafloor morphology;
- geology;
- and geophysics;
- 3060 Subduction zone processes (1031;
- 3613;
- 8170;
- 8413);
- 8104 Continental margins: convergent;
- 9340 Indian Ocean