The paleomagnetism of the Shawa Ijolite

Abstract

Oriented cores have been drilled at seven sites in ijolite exposures of the Shawa carbonatite complex, Southern Rhodesia. The ijolite has been dated at 209±16 m.y. from Rb → Sr decay. The directions of natural remanent magnetization are not consistent between sites. The ijolite proved difficult to treat by partial demagnetization in alternating fields, as instability of the direction of remanent magnetization tended to develop with demagnetizing fields only slightly larger than those required to remove isothermal magnetizations. Nevertheless, consistent directions of remanent magnetization were secured from five of the seven sites, after alternating-field treatment. On the assumption of a geocentric dipole field, the mean south magnetic pole position is 64.2°S, 85.6°E, with radius of 95 per cent confidence 14.1°. This is in excellent agreement with other Mesozoic pole positions from Africa.