A seismic refraction investigation of the Namaqualand Metamorphic Complex, South Africa

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Abstract
The Namaqualand Metamorphic Complex forms part of the Precambrian shield of southern Africa, and hosts several major base metal deposits. A long line seismic refraction experiment traversing the Complex was conducted in order to complement geological and geophysical studies of the structure and evolution of this region. Seismograms were obtained at approximately 10 km intervals along the 290 km profile. Seismic ray‐tracing techniques were used to model the travel‐time and amplitude data. It was found that the Namaqualand lower crust is comprised of a substantial proportion of intermediate velocity (6.2 to 6.9 km/s) rocks. These intermediate velocity rocks approach the surface near the midpoint of the profile. Moho was found to be at a depth of 42 km. No correlation was found between the seismic and electrical resistivity models of the crust. When the seimic velocity structure of the Middle Proterozoic Namaqualand Metamorphic Complex is compared with that of adjacent geological provinces, it is found to differ significantly from the Archaean Kaapvaal Province, but resemble the Late Proterozoic Damara Province. These differences might be attributed to variations in the principal mechanisms of crustal growth between Archaean and Proterozoic times.