Constraints on upper mantle anisotropy surrounding the Cocos slab from SK(K)S splitting

David L. Abt (1, 2) , Karen M. Fischer (1) , Geoffrey A. Abers (3) , Marino Protti (4) , Victor González (4) , Wilfried Strauch (5)

1 Department of Geological Sciences [Providence]
2 Now at ExxonMobil Exploration Company
3 LDEO - Lamont-Doherty Earth Observatory
4 Observatorio Vulcanológicoy Sismológico de Costa Rica
5 Instituto Nicaragüense de Estudios Territoriales

SKS and SKKS splitting observations are used to constrain the pattern of mantle flow in the Central American subduction zone beneath Costa Rica and Nicaragua. After removing the effects of shallow wedge anisotropy on SK(K)S waveforms, a best fitting model of anisotropy beneath the Cocos Plate and in the deeper mantle wedge is determined. Fast polarization directions and model symmetry axis orientations in both regions (as well as the shallow wedge) are dominated by roughly arc-parallel azimuths and, therefore, are not consistent with sublithospheric mantle flow entrained by the subducting Cocos Plate or simple two-dimensional corner flow in the wedge. In conjunction with geochemical data and local S splitting tomography, the SK(K)S splitting observations and anisotropy models are consistent with flow to the WNW within the mantle wedge on the Caribbean side of the Cocos Plate, possibly drawn through a slab window beneath Panama and southern Costa Rica. Anisotropy in the Pacific mantle beneath the Cocos Plate is also best explained by flow with a component that is roughly parallel to the strike of the slab, although the absolute direction of this flow is not uniquely constrained.

Domaines: Géomorphologie

David L. Abt, Karen M. Fischer, Geoffrey A. Abers, Marino Protti, Victor González, et al.. Constraints on upper mantle anisotropy surrounding the Cocos slab from SK(K)S splitting. Journal of Geophysical Research, 2010, 115, pp.06316. ⟨10.1029/2009JB006710⟩. ⟨insu-00564751⟩