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Paleomagnetism and age of the Archean Usushwana Complex, Southern Africa.

Abstract:

Paleomagnetic and 40Ar/39Ar age data are reported from the Usushwana Complex, a layered gabbro and pyroxenite intrusive exposed in Swaziland and E South Africa (26.5oS, 31.0oE) . The main gabbro body and an associated granophyre return a mean Rb/Sr whole-rock and Sm/Nd mineral age of 2875+ or -40Ma. Alternating field and thermal analysis of specimens from 18 sites (70 samples) yields a mean direction D = 304o, I = 53o, (k = 32, approx 95 = 6o). This direction is significantly different from that obtained from the approx 2100Ma Bushveld Complex. The paleomagnetic pole position calculated from the Usushwana Complex (9oN, 347oE) is significantly different from other late Archean poles. Although the Usushwana pole is close to the pole from the Palabora Igneous Complex of South Africa (1900Ma), there is no isotopic evidence indicating a thermal event of that age in the Usushwana Complex.-from Authors