Paleomagnetic and40Ar/39Ar Study of the Sinyai Dolerite, Kenya: Implications for Gondwana Assembly

New paleomagnetic and ⁴⁰Ar/³⁹Ar age data from the Sinyai metadolerite dike in central Kenya support the suggestion that the eastern portion of Gondwana was assembled during two separate orogenic events. The dike intrudes Mozambique Belt metasediments dated ≈700 Ma and was itself metamorphosed to greenschist facies at 547 ± 4 Ma. This greenschist-facies event reset the original magnetization in the rocks and occurred over a time span that included at least one field reversal. The paleomagnetic pole at 20°S, 319°E (δp = 3^∘, δm = 5^∘) augments the available paleomagnetic database for Gondwana and suggests that Gondwana assembly was completed by 550 Ma; therefore the concept of a united East Gondwana continent 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 ≈550 Ma in parts of East Gondwana, coupled with our paleomagnetic evidence for a united Gondwana at 550 Ma, led to our suggestion of a Kuunga Orogeny at this time. The Kuunga Orogeny results from the collision of Australo-Antarctica with Congo-IMSLEK.