Scientific Objectives

The acquisition of multibeam data and further analysis of structural style in the accretionary wedge and of the relations between outboard subduction and inboard strike-slip systems is essential to understand margin segmentation and subduction processes along this remote oblique convergent continental margin.

The expected results of the proposed activity (acquisition of multibeam data and structural analysis based on pre-stacked depth migrated seismic lines) should give an answer to the following questions:

• what are the relationships between the shallow crustal deformation, the stress regime along the margin and the subduction process? What are the crustal thicknesses in the subduction complex? Are there high seismic velocity bodies which may correspond to ophiolitic complexes emplaced during the subduction of the Chile Rise? What are the extent of the recenmost wedge and rates of accretion?

• where is the Antarctic/Scotia/South America triple junction located? Is deformation at the triple junction diffuse or localised?

• a high structural variability has been pointed out by the analysis of the existing multichannel seismic data; is it effectively the result of the subdivision of the margin into different rotating crustal blocks as described on land? Are there strike slip faults oblique to the margin that can be seen on morpho-bathymetric data? Do these faults control the variation in the depth of the dècollement level observed on seismic profiles?

• What is the thermal regime within the accretionary complex? Why is the BSR more continuous where the dècollement is deeper? What are the relationships between tectonics and fluid flow within the wedge?

To reach these main objectives we propose to analyse in more details the following issues:

• - comparison between the structural setting of the margin north of 53S where subduction is orthogonal and south of 53S where obliquity progressively increases. Because of its highly oblique convergence, the Chilean margin south of the Strait of Magellan represents an end-member style of subduction about which very little is known.

• - Identification and mapping of all the structural lineaments along the margin based on the interpretation of multibeam data, in order to obtain a detailed fault map and to provide 3-dimensional images of the subduction complex.

• - depth sections along the available multichannel seismic profiles in order to define crustal thicknesses across the subduction complex through the pre-stack depth migration of some multichannel seismic data as well as gravity modeling.

• - seismo-stratigraphyc analysis of the sediments in the forearc basin to test the interplay between tectonic uplift in the accretionary wedge, sediment supply and subsidence in the forearc basin

• - Relationships between tectonics and fluid flow in the accretionary complex

• - Analysis and modelling of the geothermal gradients within the accretionary complex through the BSR.

• - Analysis of the wavelet attributes of the BSR and their variations inside the complex.