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Single-grain and conventional zircon dating of remobilized basement gneisses in the central Damara belt of Namibia

Abstract:

The southwest-central Damara belt contains a variety of granitoid gneisses which have previously been correlated with the ~2 Ga old Abbabis Inlier and which have been subjected to strong structural overprinting and migmatization during the late Precambrian Damara orogeny. Zircons have been dated using the ion microprobe SHRIMP and conventional dissolution techniques, from two samples of migmatized quartzo-feldspathic orthogeneiss collected at localities in the lower Khan River near Rossing Uranium Mine. It is surprising that Damar metamorphism and magmatization left little or no imprint on the zircons analyzed. The 1040-1100 Ma ion microprobe single zircon ages for the first time demonstrate the existenceof a pre-Damara basement distinct from, and considerably younger than, the Abbabis Complex. It is tentatively suggested that this basement represents a northwest extension of the Rehoboth terrain, and in this case there may have been continuity of pre-Damara continental crust underneath the southern Damara belt. -from Authors