Anisotropy beneath Iceland: Using splitting observations to constrain mantle flow

Mei Xue and Richard M. Allen
University of Wisconsin-Madison

AGU Fall Meeting 2003

Anisotropy beneath Iceland provides important clues to the interaction of the Iceland plume and Mid-Atlantic ridge. In this study, we combine the HOTSPOT and SIL datasets and select 28 events for SKS splitting analysis. Measurements were made at 35 stations using Wolfe and Silver (1998)’s multi-event stacking procedure. Our observed splitting directions are generally consistent with those of Bjarnason and Silver (2002) from the ICEMELT experiment. However the denser station coverage reveals a different anisotropic signature in central Iceland. Our splitting results fall into three groups: (1) Eastern Iceland: the average fast polarization directions is N17?W with an average delay time of 1.21 sec; (2) Central Iceland: the average fast polarization directions is N43?W with an average delay time of 1.60 sec; (3) Western Iceland: weaker anisotropy (average delay time 0.57 sec) with less well-constrained fast polarization directions. These observations suggest that the plume-ridge interaction does not dominate the anisotropic pattern; instead the splitting results are mainly attributed to shear of the North American and Eurasian plate motion relative to a background mantle flow with a direction of S10?E and a magnitude of approximately 20 mm/yr in the hotspot reference frame. The absence of anisotropy in western Iceland may suggest a strong vertical heterogeneity beneath western Iceland, and the splitting observations may be more reflective of the fast polarization directions of the lithosphere or crust. This heterogeneity may be caused by the complex lithosphere-asthenosphere boundaries that disturb the asthenosphere flow beneath Western Iceland.