PALEOMAGNETIC INVESTIGATION OF THE NEOPROTEROZOIC GAGWE LAVAS AND MBOZI COMPLEX, TANZANIA AND THE ASSEMBLY OF GONDWANA

The 810 Ma Gagwe-Kabuye lavas and the 743 Ma Mbozi gabbro-syenite complex of the Congo Craton in East Africa were sampled for paleomagnetic study in an effort to test a variety of tectonic models proposed for Neoproterozoic times. The paleomagnetic pole obtained from the Gagwe-Kabuye lavas falls at 25 degrees S, 273 degrees E (delta p = 7 degrees, delta m = 12 degrees) and compares favorably to a previously published paleomagnetic pole obtained from these rocks. The Mbozi complex pole yields a paleomagnetic pole at 46 degrees N, 325 degrees E (delta p = 5 degrees, delta m = 9 degrees) and differs significantly from a previously determined pole for the Mbozi complex. A comparison of these paleomagnetic poles to Laurentian poles of the same age suggests that the Congo Craton may not have constituted part of the Rodinia supercontinent in the configuration proposed by Dalziel (1992). An analysis of reliable paleomagnetic poles from the Gondwana blocks for the interval from 810 to 510 Ma reveals a coherent swathe of poles from 550 to 510 Ma and a scatter of pre-600 Ma poles. Our interpretation of the available paleomagnetic and tectonic data for this interval is consistent with the formation of Gondwana by two distinct orogenic events. This assembly resulted in the East Africa Orogen between 800 and 650 Ma and a younger Kuunga Orogen at 550 Ma outboard of the East Africa Orogen with possible sutures located in Sri Lanka, southern India and Enderby Land (East Antarctic Craton).