New Meso-Neoproterozoic Paleomagnetic Results from the Congo-Sao Francisco Craton

English Abstract:

The Congo-Sao Francisco (SF) craton is a keystone of Gondwana and also a possible part of the Precambrian supercontinent Rodinia, but its movement through Meso-Neoproterozoic time still remains mostly unconstrained due to sparsity of reliable paleomagnetic data. Paleomagnetic results from 1.4 to 0.6 Ga igneous rocks, spanning southern Congo-SF from Tanzania to Namibia and eastern Brazil, help define a new apparent polar wander path for the craton. The youngest rocks in our paleogeographic reconstruction, the Sanyika redbeds of Tanzania, are still under geochronological investigation, but detrital zircon analyses demonstrate sedimentation ages of less than ~684 Ma. Five sites within the redbeds yield a shallow ESE-WNW dual-polarity remanence direction held by hematite. Together with published data from the Gagwe lavas, Mbozi Complex, and Luakela volcanics, our new data suggest complicated motions of Congo-SF craton through the Tonian-Cryogenian interval. These results are combined with a key pole from Brazil dated at 920 Ma, which is used to better define continuous motion of the craton relative to Laurentia and Baltica. We also sampled Mesoproterozoic rocks from three different geological units in northern Namibia. The oldest of these is the Kunene Anorthosite Complex, dated at ~1370 Ma. In the southern Kunene area, the anorthosite complex is intruded by Epembe syenites (~1220 Ma) and related dolerite dykes, and in the eastern area near Swartbooisdrif, the anorthosite is intruded by both dolerite and carbonatite dykes (~1130 Ma). Initial results from Namibia appear promising, including a possible positive baked-contact test for a Swartbooisdrif dyke intruding Kunene anorthosite. All of the new results are incorporated into an animation of Congo-SF motion through Mesoproterozoic Nuna breakup to terminal Proterozoic-Cambrian Gondwana assembly.