Subduction system and flat slab beneath the Eastern Cordillera of Colombia (original) (raw)
ADS
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- De Gori, Pasquale ;
- Faccenna, Claudio ;
- Speranza, Fabio ;
- Seccia, Danilo ;
- Dionicio, Viviana ;
- Prieto, Germán. A.
Abstract
Seismicity at the northern terminus of the Nazca subduction is diffused over a wide area containing the puzzling seismic feature known as the Bucaramanga nest. We relocate about 5000 earthquakes recorded by the Colombian national seismic network and produce the first 3-D velocity model of the area to define the geometry of the lithosphere subducting below the Colombian Andes. We found lateral velocity heterogeneities and an abrupt offset of the Wadati-Benioff zone at 5°N indicating that the Nazca plate is segmented by an E-W slab tear, that separates a steeper Nazca segment to the south from a flat subduction to the north. The flat Nazca slab extends eastward for about 400 km, before dip increases to ∼50° beneath the Eastern Cordillera, where it yields the Bucaramanga nest. We explain this puzzling locus of intermediate-depth seismicity located beneath the Eastern Cordillera of Colombia as due to a massive dehydration and eclogitization of a thickened oceanic crust. We relate the flat subducting geometry to the entrance at the trench at ca. 10 Ma of a thick - buoyant oceanic crust, likely a volcanic ridge, producing a high coupling with the overriding plate. Sub-horizontal plate subduction is consistent with the abrupt disappearance of volcanism in the Andes of South America at latitudes > 5°N.
Publication:
Geochemistry, Geophysics, Geosystems
Pub Date:
January 2016
DOI:
Bibcode:
Keywords:
- seismic tomography;
- Colombian Andes;
- subduction