Shear wave anisotropy in northwestern South America and its link to the Caribbean and Nazca subduction geodynamics

Javier Idarraga Garcia*, J M Kendall, C.A. Vargas

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

14 Citations (Scopus)
513 Downloads (Pure)

Abstract

To investigate the subduction dynamics in northwestern South America, we measured SKS and slab-related local S splitting at 38 seismic stations. Comparison between the delay times of both phases shows that most of the SKS splitting is due to entrained mantle flow beneath the subducting Nazca and Caribbean slabs. On the other hand, the fast polarizations of local S-waves are consistently aligned with regional faults, which implies the existence of a lithosphere-confined anisotropy in the overriding plate, and that the mantle wedge is not contributing significantly to the splitting. Also, we identified a clear change in SKS fast directions at the trace of the Caldas Tear (~5°N), which represents a variation in the subduction style. To the north of ~5°N fast directions are consistently parallel to the flat subduction of the Caribbean plate-Panama arc beneath South America, while to the south fast polarizations are subparallel to the Nazca-South America subduction direction. A new change in the SKS splitting pattern is detected at ~2.8ºN, which is related to another variation in the subduction geometry marked by the presence of a lithosphere-scale tearing structure, named here as Malpelo Tear; in this region, NE-SW-oriented SKS fast directions are consistent with the general dip direction of the
underthrusting of the Carnegie Ridge beneath South America. Further inland, this NE-SW-trending mantle flow continues beneath the Eastern Cordillera of Colombia and Merida Andes of Venezuela. Finally, our results suggest that the sub-slab mantle flow in northwestern South America is strongly controlled by the presence of lithospheric tearing structures.
Original languageEnglish
Pages (from-to)3655–3673
Number of pages19
JournalGeochemistry, Geophysics, Geosystems
Volume17
Issue number9
Early online date15 Sep 2016
DOIs
Publication statusPublished - 27 Oct 2016

Keywords

  • Lithospheric tearing
  • Mantle flow
  • Northwestern South America
  • S-wave splitting
  • Seismic anisotropy
  • Subduction geodynamics

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