ANISOTROPIC UPPER-MANTLE STRATIGRAPHY AND ARCHITECTURE OF THE SLAVE CRATON

The Earth's physical properties show a dominantly radial structure whi ch is the result of compositional differentiation, isochemical phase c hanges(1) and rheological layering(2). Rheological layering is perhaps the most difficult to investigate using conventional seismological te chniques because the seismic manifestation of this property, elastic a nisotropy, may closely mimic the effects of isotropic heterogeneity(3) . Nonetheless, an improved characterization of Earth's rheological str ucture promises important insights into such processes as plate dynami cs and continental evolution. Here, I present a methodology for effect ively characterizing sharp transitions in anisotropic, upper-mantle st ructure using the coda of teleseismic P-waves. Application to seismogr ams from the Slave craton reveals a well-developed stratigraphy, at le ast in part anisotropic, with major boundaries occurring at nominal de pths of 75, 135 and 195 km. The geometry and sharpness of these discon tinuities suggest a structural origin, perhaps involving shallow subdu ction.