abstract
Rb-Sr and Sm-Nd whole-rock data are presented for the Jutulsessen granitic gneiss, deformed intrusive mafic dykes, and cross-cutting pegmatites and aplites. The data indicate that Nd-isotopic homogenisation last occurred at ?1 153 Ma, whereas Sr-isotopic homogenisation last occurred at ?535 Ma. Both ages are significant in that they correspond to widely recognised periods of tectonothermal activity, namely the latest Kibaran orogeny and the late Ross (or Pan-African) orogeny. The age discrepancy is attributed to isotopic decoupling of the Rb-Sr system from the Sm-Nd system during the Late Cambrian. The intrusive age of the Jutulsessen granitic suite is interpreted to be ?1 153 Ma, and the combined Sr and Nd data suggest that it was derived from a mantle-type source (I-type), or from juvenile sediments with short crustal residence times. The isotopic data also imply that the observed structural D1, and D2 events at Jutulsessen are Proterozoic in age, and the D3 event is Late Cambrian. Comparison of these data with other areas of the East Antarctic craton and elsewhere indicate that the Early Cambrian Ross orogeny extensively reactivated on older Kibaran orogenic belt, but that the effects of this reactivation are variable and difficult to characterise from one area to another.
