Mantle discontinuities under southern Africa from precursors to P′ P′_df

Abstract

Abstract.We investigate the reflection properties of uppermantle discontinuities beneath southern Africa using precursors to the df branch of PKPPKP (P'P'). The P'P' df branch is

The orthorhombic to high‐P monoclinic phase transition in Mg‐Fe Pyroxenes: Can it produce a seismic discontinuity?

“…A small jump in seismic velocities at 4300 km depth, recently designated the "X discontinuity", has been occasionally observed in seismic profiles from along the western margin of the Pacific Ocean, under northern Australia, and from under southern Africa [Hales et al, 1980;Leven, 1985;Revenaugh and Jordan, 1991;Xu et al, 1998]. The profiles sample subcontinental lithospheric mantle under Africa and Australia, and the region around subduction zones [Revenaugh and Jordan, 1991], locations which are consistent with the expected occurrence of abundant depleted mantle [Ringwood, 1975;Jordan, 1978;Davidson, 1996].…”

Deep Earth Structure - Transition Zone and Mantle Discontinuities

“…Bostock (1996a) found also in Ps data a sharper 410 than 660 beneath the North American craton. Xu et al (1998) and Xu et al (2003) found globally a sharp 660 (2 km or less) and a less sharp 410 from P 0 P 0 precursors. Neves et al (2001) found a 10 km sharp 410 and a 5 km sharp 660 beneath North America in wide-angle data.…”

“…Steep-angle techniques (see Chapter 1.08), which are more suited for determining smallscale topography of the mantle discontinuities, include ScS reverberations (e.g., Jordan, 1987, 1991a,b); SS, P 0 P 0 , and PP precursors (e.g., Adams, 1968Adams, , 1971Bolt, 1970;Engdahl and Flinn, 1969;King et al, 1975;Shearer, 1991Shearer, , 1993Whitcomb and Anderson, 1970;Zheng and Romanowicz, 2012); and Ps and Sp conversions at the discontinuities (receiver functions, e.g., Bath and Stefansson, 1966;Benz and Vidale, 1993;Chevrot et al, 1999;Faber and Mü ller, 1980;Li et al, 2003a;Stammler et al, 1992;Vinnik, 1977;Xu et al, 1998; see Figure 1 for ray paths of such phases). This technique is however less suited for determining their small-scale topography, because the lateral part of the travel path of wide-angle rays is several times longer than the vertical part.…”

Deep Earth Structure – Transition Zone and Mantle Discontinuities

“…Neves et al (2001) found a 10 km sharp 410 and a 5 km sharp 660 beneath North America from wideangle data. Xu et al (1998) found a sharp 660 and a less clear 410 from P9P9 precursors reflected beneath South Africa. Song et al (2004) found in the northwestern US a 20-90 km thick low velocity zone above the 410 from wide-angle data, which they interpret as indication of high water content in the transition zone (Bercovici and Karato, 2003).…”

“…Steep-angle techniques (see Chapter 1.08), more suited for determining small-scale topography of the mantle discontinuities, are ScS reverberations (e.g., Revenaugh and Jordan, 1987, 1991a, 1991b, SS, P9P9, andPP precursors (e.g., Shearer, 1991, 1993;Adams, 1968Adams, , 1971Whitcomb and Anderson, 1970;Engdahl and Flinn, 1969;Bolt, 1970;King et al, 1975), or Ps and Sp conversions at the discontinuities (e.g., Båth and Stefansson, 1966;Vinnik, 1977;Faber and Müller, 1980;Stammler et al, 1992;Benz and Vidale, 1993;Xu et al, 1998;Chevrot et al, 1999;Li et al, 2003a; see Figure 1 for ray paths of such phases). This technique is however less suited for determining their small-scale topography.…”