Ridge subduction along the central Chilean margin: Insights from seismic and bathymetric studies
Abstract
The central Chilean margin was the target of RV SONNE cruise SO161. Here we present preliminary results of the seismic and swath surveys across the subduction zone and volcanic structures entering the trench. The subduction process is characterized by a change in dip angle of the downgoing plate, resulting in a segmentation of the margin. Segment boundaries commonly coincide with bathymetric elevations, ridges, or fracture zones on the oceanic plate. The effects of ridge subduction on the margin suggest a linkage of the subducting Juan Fernandez chain on the Nazca plate to the flat slab segment of the central Chilean margin. The Chile subduction zone is unique in that the growth and destruction of the margin may be observed in regions of subduction accretion and subduction erosion, respectively. The study area covers the eastern part of the aseismic Juan Fernandez Ridge and the continental slope off Valparaiso. Two coincident wide-angle and reflection seismic profiles are located across the subduction complex. Towards the trench, a wedge-shaped body of reduced velocities is observed and interpreted as accreted, compressed, and reworked trench material. A backstop probably consisting of Paleozoic basement is clearly defined by the high p-wave velocities ranging from 5.3 km/s to 6.0 km/s. In contrast to the landward part of the profile, the Moho is clearly visible on the seaward side of the trench, at a depth of about 11 km. The crustal structure of the O'Higgins seamount group is the target of tomographic investigations using two perpendicular cross lines of high ray coverage resulting from a dense instrument spacing of ca. 2.2 nm. The tomographic inversion scheme includes a first-arrival inversion process, which has been modified to also consider later arrivals. The aim of the study is to determine the rate of underplating and the ratio of extrusive vs. intrusive melt generated when the plate moved over the hotspot, which formed the Juan Fernandez Ridge.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2002
- Bibcode:
- 2002AGUFM.T62B1315K
- Keywords:
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- 3025 Marine seismics (0935);
- 8015 Local crustal structure;
- 8105 Continental margins and sedimentary basins;
- 8180 Tomography;
- 9360 South America