Seismic anisotropy and shear wave splitting associated with mantle plume‐plate interaction

Abstract

Geodynamic simulations of the development of lattice preferred orientation in the flowing mantle are used to characterize the seismic anisotropy and shear wave splitting (SWS) patterns expected for the interaction of mantle plumes and lithospheric plates. Models predict that in the deeper part of the plume layer ponding beneath the plate, olivine a axes tend to align perpendicular to the radially directed plume flow, forming a circular pattern reflecting circumferential stretching. In the shallower part of the plume layer, plate shear is more important and the a axes tend toward the direction of plate motion. Predicted SWS over intraplate plumes reflects the asymmetric influence of plate shear with fast S wave polarization directions forming a pattern of nested U shapes that open in the direction opposing both plate motion and the parabolic shape often used to describe the flow lines of the plume. Predictions explain SWS observations around the Eifel hot spot with an eastward, not westward, moving Eurasian plate, consistent with global studies that require relatively slow net (westward) rotation of all of the plates. SWS at the Hawaiian hot spot can be explained by the effects of plume-plate interaction, combined with fossil anisotropy in the Pacific lithosphere. In ridge-centered plume models, the fast polarization directions angle diagonally toward the ridge axis when the plume is simulated as having low viscosity beneath the thermal lithosphere. Such a model better explains SWS observations in northeast Iceland than a model that incorporates a high-viscosity layer due to dehydration of the shallow-most upper mantle.

Deformation in the asthenospheric mantle beneath the Carpathian‐Pannonian Region

“…Shear wave splitting observations at the Eifel hot spot in Germany are consistent with this prediction [ Walker et al , ]. However, that observation and also numerical prediction [ Ito et al , ] differ from our splitting data. The NW‐SE anisotropy does not agree with the expected anisotropy (parabolic pattern) from a mantle upwelling.…”

“…In this model an active mantle plume would provide extension driving forces. If we assume that we observe the ascent of a plume in the S K S splitting measurements, the pattern of anisotropy should depict a parabolic flow at the base of the lithosphere as a result of interaction between extension, mantle upwelling, and plate motion [ Sleep , ; Ito et al , ]. Shear wave splitting observations at the Eifel hot spot in Germany are consistent with this prediction [ Walker et al , ].…”

Waveform modeling of shear wave splitting from anisotropic models in Iceland

“…Here the flow pattern is still radial but the vertical shear because the lithosphere is small; the dominant deformation is one of contraction in the radial (the flow slows with radial distance) and vertical directions (the plume is thinning with radial distance), and circumferential elongation (flow lines are diverging). This circumferential stretching causes the olivine a-axes to preferentially align circumferentially and orthogonal to the flow [Ito et al, 2011]. This result was also seen in recent laboratory experiments of plumes [Druken et al, 2011].…”

Origins of cratonic mantle discontinuities: A view from petrology, geochemistry and thermodynamic models

“…Griffin et al, 1999Griffin et al, , 2004Arndt et al, 2009). Vertical lineation in the plume stem gives way to horizontal lineation when the plume impinges upon the LAB (Ito et al, 2014). Dipping lineations may result when material flows laterally towards thinner craton margins (Sleep, 2002;Shervais and Hanan, 2008).…”