A Geophysical Survey of the Interaction between the Chile Ridge and Chile Trench

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This is a major geophysical field program to survey the southern Chile margin where a mid-ocean spreading ridge (Chile Ridge) is being subducted along the Chile Trench (Chile Triple Junction). Collected will be multichannel seismic reflection data, SEABEAM bathymetric data, gravity data and dredge samples. The principal scientific objectives of this survey are 1) to test models for the tectonic effects of ridge crest subduction, and 2) study subduction processes under the extremal conditions of a ridge-trench collision. This area is a unique tectonic setting and perhaps the best place in the world to study this interaction. Here, over a short distance straddling the triple junction, it is possible to study what happens before, during, and after the subduction of an active spreading center. Specific objectives involve comparing the deep structure, surficial morphology, and tectonic fabric of the inner-trench wall in zones corresponding to conditions before, during and after ridge-trench collision. To address these objectives data will be collected, processed and analyzed from four different transects or corridors across the trench. These data will provide the necessary information for planning and developing specific drilling objectives and drill sites for future ODP drilling in the area. They also will be used for interpreting and extrapolating drilling results in a regional tectonic context.