|From the desk of Bruce Wilkinson:
|"Our own Scott Samson (and colleagues at Cornell University, Université de Lomé, Lomé, and the University of Ghana) have authored a very interesting paper that just appeared in the Journal of African Earth Sciences entitled: “Geochemical Characteristics and U-Pb Zircon LA-ICPMS Ages of Granitoids from the Pan-African Dahomeyide Orogen, West Africa”.
The gist of the thing is that the Dahomeyide orogen in southeastern Ghana is the suture to the West African Craton to northwest. Granitoids to the east of the suture zone are postulated to be an arc terrane that formed during subduction and oceanic closure. Scott and his colleagues mapped these granitoids in Ghana, Togo, and Benin, which allowed them to distinguish between a migmatitic and a dioritic gneiss, separated by a segment of the Trans-Saharan shear zone that extends for ~2500 km from the Sahara to the Gulf of Guinea. U-Pb zircon ages from the migmatitic gneiss ranging from 615 to 589 Ma, similar to the metamorphic age of the suture zone rocks, while zircons from the dioritic gneiss yield U-Pb ages ranging from 2.19 to 2.14 Ga, the first reported Paleoproterozoic rocks west of the Kandi fault zone. Nd model ages of rocks in the suture zone suggest the widespread involvement of older crust in the Pan-African collision zone, similar to isotopic data from the correlative Medio Coreau domain of the northwest Borborema province in Brazil."