Moho depth and sediment thickness estimates for the coastal basins of southeastern Tanzania and the Mozambique Coastal Plain

Abstract

We investigate crustal structure in the southeastern coastal basins of Tanzania and the Mozambique Coastal Plain (MCP), which formed during the breakup of Gondwana, using P-wave receiver functions and Rayleigh wave dispersion measurements. Sediment thicknesses, Moho depths, and the amount of crustal thinning that occurred during basin formation along the passive margin of eastern Africa are poorly known. Also, for the MCP, the nature of the crust, whether it is stretched continental crust, oceanic crust or transitional crust remains uncertain. Results from 13 seismic stations in the MCP reveal sediment thicknesses ranging from four to nine km and Moho depths ranging from 24 to 37 km, with an average of 28 km. The average crustal shear wave velocities for stations in the MCP range from 3.6 to 3.7 km/s, indicating the crust is of continental origin and not oceanic. In addition, we find little evidence for high velocity mafic layers in the MCP crust, as would be expected for oceanic crust. Assuming a crustal thickness of 37 km for the MCP prior to thinning yields a crustal stretching (β) factor of ∼1.7. Results from six seismic stations in the coastal basins of southeastern Tanzania reveal sediment thicknesses ranging from four to six km and Moho depths ranging from 25 to 34 km, with an average of 30 km. Assuming a crustal thickness of 38 km for southeastern Tanzania prior to thinning yields a crustal stretching (β) factor of ∼1.5. This finding, when combined with the β factor for the MCP, suggests similar amounts of crustal stretching along much of the eastern African passive margin.