Publication Date:
2014-02-19
Description:
[1] We study the erosive convergent margin of north-central Chile (at ~31°S) by using high-resolution bathymetric, wide-angle refraction, and multichannel seismic reflection data to derive a detailed tomographic 2D velocity-depth model. In the overriding plate, our velocity model shows that lowermost crustal velocities beneath the upper continental slope are 6.0-6.5 km/s, which are interpreted as the continental basement composed by characteristic metamorphic and igneous rocks of the Coastal Cordillera. Beneath the lower and middle continental slope, however, the presence of a zone of reduced velocities (3.5–5.0 km/s) is interpreted as the outermost forearc composed of volcanic rocks hydrofractured as result of frontal and basal erosion. At the landward edge of the outermost forearc, the bathymetric and seismic data provide evidence for the presence of a prominent trenchward-dipping normal scarp (~1 km offset), which overlies a strong lateral velocity contrast from ~5.0 to ~6.0 km/s. This pronounced velocity contrast propagates deep into the continental crust, and it resembles a major normal listric fault. We interpret this seismic discontinuity as the volcanic-continental basement contact of the submerged Coastal Cordillera characterized by a gravitational collapse of the outermost forearc. Subduction erosion has, most likely, caused large scale crustal thinning and long term subsidence of the outermost forearc.
Print ISSN:
0094-8276
Electronic ISSN:
1944-8007
Topics:
Geosciences
,
Physics
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