Seismic structure of the north-central Chilean convergent margin: Subduction erosion of a paleomagmatic arc

Eduardo Contreras-Reyes, Juan Becerra, Heidrun Kopp, Christian Reichert, JUAN LORENZO DIAZ NAVEAS

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25 Scopus citations

Abstract

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 2-D velocity-depth model. In the overriding plate, our velocity model shows that the 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 fore arc composed of volcanic rocks hydrofractured as a result of frontal and basal erosion. At the landward edge of the outermost fore arc, 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 fore arc. Subduction erosion has, most likely, caused large-scale crustal thinning and long-term subsidence of the outermost fore arc. Key Points Our results have implications for subduction erosion A major velocity discontinuity is detected beneath the middle continental slope Possible gravitational collapse of the outermost fore-arc block off north Chile

Original languageEnglish
Pages (from-to)1523-1529
Number of pages7
JournalGeophysical Research Letters
Volume41
Issue number5
DOIs
StatePublished - 16 Mar 2014
Externally publishedYes

Keywords

  • Chile
  • gravitational collapse
  • hydrofracturing
  • subduction
  • subduction erosion

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