PALEOMAGNETIC AND AR-40 AR-39 STUDY OF THE SINYAI DOLERITE, KENYA - IMPLICATIONS FOR GONDWANA ASSEMBLY/

New paleomagnetic and Ar-40/Ar-39 age data from the Sinyai metadolerit e dike in central Kenya support the suggestion that the eastern portio n of Gondwana was assembled during two separate orogenic events. The d ike intrudes Mozambique Belt metasediments dated approximate to 700 Ma and was itself metamorphosed to greenschist facies at 547 +/- 4 Ma. T his greenschist-facies event reset the original magnetization in the r ocks and occurred over a time span that included at least one field re versal. The paleomagnetic pole at 20 degrees S, 319 degrees E (delta p = 3 degrees, delta m = 5 degrees) augments the available paleomagneti c database for Gondwana and suggests that Gondwana assembly was comple ted by 550 Ma; therefore the concept of a united East Gondwana contine nt may not be valid for pre-550 Ma time. In our model, the 650-800 Ma East Africa Orogeny resulted from a collision between the Congo craton of East Africa and the IMSLEK terranes (India, Madagascar, Sri Lanka, Enderby Land, and the Kalahari craton). A pervasive granulate-facies metamorphis event at approximate to 550 Ma in parts of East Gondwana, coupled with our paleomagnetic evidence for a united Gondwana at 550 M a, led to our suggestion of a Kuunga Orogeny at this time. The Kuunga Orogeny results from the collision of Australo-Antarctica with Congo-I MSLEK.