Seismic Characteristics of the Pan-African Granulite Terranes of Southern Gondwanaland

The Pan-African orogeny was a major tectono-thermal event which occurred at the Proterozoic-Palaeozoic boundary (~600 Ma) and is now marked by zones of high-grade metamorphism distributed from the Arabian-Nubian shield through Tanzania, Mozambique, Southern India and Sri Lanka to the eastern Antarctic. Teleseismic earthquake recordings from stations in these areas have been analyzed to compare the seismic characteristics of the crust and upper mantle for these regions. Inversion of P-wave receiver functions and surface-wave phase velocity data reveals a similar crustal structure in each of these areas of the now disrupted Pan-African belt. The Pan-African crust has a more complicated structure than does the adjacent Eastern Dharwar Craton of the south Indian shield. Most of the stations located on the Pan-African granulite terranes show a two-layer crust with a clear mid-crustal discontinuity and a lower velocity zone at upper to mid-crustal depths. The analysis of the splitting of Ps Moho converted phases indicates similar anisotropic fabric for the crust when considering their reconstructed locations. SKS splitting measurements show a similar anisotropic fabric for the upper mantle beneath the stations whose data we have analyzed. Both the crust and upper mantle anisotropy for the Pan-African granulite terranes is significantly different from that observed on the Eastern Dharwar Craton of the south Indian shield.