Converted waves reveal a thick and layered tectosphere beneath the Kalahari super-craton

Details Converted waves reveal a thick and layered tectosphere beneath the Kalahari super-craton Converted waves reveal a thick and layered tectosphere beneath the Kalahari super-craton

Feb 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007e%26psl.254..404w&link_type=abstract

Earth and Planetary Science Letters, Volume 254, Issue 3-4, p. 404-415.

Physics

14

Scientific paper

Thick and high-velocity roots are generally observed beneath the Archean cratons. Inside these high-velocity keels, velocity contrasts are detected neither by surface nor by body waves tomographies. We present here evidences based on the S-to-P and P-to-S converted waves for the existence of an irregularly stratified and thick keel beneath the Kalahari super-craton. To satisfy surface wave data and S-to-P conversions, the velocity model should have beneath the Moho a ˜ 160 km thick anisotropic structure with vertical slow axis and decreasing anisotropic parameters with depth. Such a structure may stem from the preferred orientation of olivine [100] axis in the horizontal plane under shearing deformation. This structure, together with the ˜ 100 km thick layer underlying it, forms a ˜ 300 km thick continental root beneath the cratons. Inside this root, the P and S velocities should be higher on average respectively by an amount of 6% and 4% than the AK135 velocity model. Beneath ˜ 300 350 km depth, a low velocity zone is clearly detected that may be either the remainder of large magma reservoirs related to cratonic flood basalts or a melted silicate layer created by the transformation, just above the 410-km deep discontinuity, of wadsleyite assembly to olivine assembly.

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