International Geologiical Congress - Oslo 2008

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STT-07 Three-dimensional aspects of subduction zone processes: Insight from dynamic modelling, tectonic reconstructions and obse

 

Structural styles of the Timor Trough subduction zone based on 2D seismic data interpretation

 

Mateus Da Costa, University of Stavanger (Norway)
Alejandro Escalona, University of Stavanger (Norway)
 

 

The Timor Trough, located between northwestern Australia and Timor Island, is the deep water expression part of the elongated trench formed by subduction between the Australian continental passive margin and the Banda arc and Savu forearc basin (both part of the Eurasian plate). By integrating approximately 250 km of 2D seismic data along the East Timor territorial waters, integrated with wells, regional geology and three-dimensional visualization, we attempt to reconstruct the different phases of deformation and structural styles in the Timor Trough.

Seismic interpretation along the Timor Trough reveals four main zones of deformation, from south to north:

1) a major rifted basin of pre-Cenozoic age trending NW-SE and NE-SW, situated in the Australian continental margin. This rifted basin represents the various phases of extension recorded on the Australian continental margin from Silurian to Cretaceous, caused by rifting of the Australian and Eurasian plates. About 8 kilometers thick of sediments, clastics and carbonate rocks, were deposited during the synrift and post rift phases of deformation; 2) an uplifted area, between the stable passive margin and the Timor trough trench area, is interpreted as a flexural forebulge of Paleogene-Recent age. The forebulge is formed as a flexural response of bending the thick Australian continental margin beneath the Savu forearc basin. Preliminary mapping of the main stratigraphic intervals reveals a complex thinning and thickening of sedimentary units that suggests a complex interaction between the forebulge migration pattern as convergence occurred, and sources of sedimentation; 3) Recent normal faulting, parallel to the subduction zone, mainly dipping north, between the forebulge area and the accretionary prism. Normal faulting is interpreted as a direct effect of flexural bending caused by subduction, resulting in tectonic loading of the Banda Arc and Savu forearc basin over the Australian continental passive margin. Even though our interpretation shows mostly Neogene-Recent faulting, we suggest that most Paleogene faulting have been consumed by the subduction zone or have been reactivated. Similar to the forebulge area, thinning and thickening of the different sedimentary units reveals a complex interaction between the flexural response of the Australian continental margin and the source of sedimentation; and 4) the Timor accretionary prism area, which is built of scrapped-off sediments from the Australian continental margin since the late Paleogene. The Australian slab can be traced for several kilometers beneath the accretionary prism. Due to the structural complexity and chaotic character of the seismic reflections, the accretionary prism itself is very difficult to interpret. However, a backstop type of structure is observed close to the edge with Timor Island, probably representing the boundary between the Savu forearc basin and the Australian continental plate.

 

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