HR: 0830h
AN: S11C-0315    [PDF]
TI: Lithopsheric anisotropy in the Archean Slave craton, Canada
AU: * Snyder, D B
EM: dsnyder@nrcan.gc.ca
AF: Geological Survey of Canada, 615 Booth Street, Ottawa,, ON K1A 0E9 Canada
AU: Bostock, M
EM: bostock@eos.ubc.ca
AF: Dept. of Earth & Ocean Sciences, University of British Columbia, 129-2219 Malin Mall, Vancouver, BC V6T 1Z4 Canada
AU: Lockhart, G D
EM: grant.d.lockhart@bhpbilliton.com
AF: BHP-Billiton Diamonds Inc., 1699 Powick Road, Kelowna, BC V1X 4L1 Canada
AB: Shear wave anisotropy and discontinuity studies of teleseismic earthquakes recorded at single seismic stations help to define vertical mantle stratigraphic columns. Beneath the Archean outcrops of the central Slave craton seismic discontinuities at 38, 115, 140, and 190 km appear to bound two distinct anisotropic layers. The discontinuity at 38 km is the Moho; discontinuities at 110-120 and 140-150 km depths observed at multiple nearby stations indicate that a layer of low velocity or distinct anisotropy exists between these depths. The coherent pulses at about 13 seconds on the radial component indicates a strong decrease in velocity at 110 km depth north and west of the Ekati diamond mine, but not to the south. The response on the transverse component indicates a rotation of anisotropic fabric at 117 km depth, a reversal at 140 km, and another rotation at 190 km. A flip in polarity at a back azimuth of about 280$\deg$ occurs in the 117 km discontinuity and apparently marks an axis of symmetry of anisotropy, here probably the dip direction of steep layering or planar fabric. SKS anisotropy studies at this station indicate that the upper of two anisotopic layers has a fast-axis direction of 010$\deg$. Geochemical studies of xenolith samples from nearby kimberlites suggest that the boundaries at 115 and 140 bound a layer of ultra-depleted harzburgite, almost pure olivine, that formed as oceanic crust.
DE: 5100 PHYSICAL PROPERTIES OF ROCKS
DE: 7203 Body wave propagation
DE: 7260 Theory and modeling
DE: 8025 Mesoscopic fabrics
DE: 8110 Continental tectonics--general (0905)
SC: Seismology [S]
MN: 2003 Fall Meeting