Two stages of zircon and monazite growth in anatectic leucogneiss: SHRIMP constraints an the duration and intensity of Pan-African metamorphism in Prydz Bay, East Antarctica

SHRIMP U-Pb data from two samples of foliated anatectic leucogneiss bracket the high-grade metamorphic history of metasediments from southern Prydz Bay, East Antarctica. Magmatic zircons in these two samples have mean crystallization ages of 535 +/- 13 and 536 +/- 35 Myr, and provide a good estimate for the timing of peak metamorphism and partial melting. Low-Th monazite grains in the same samples have mean ages of 528 +/- 4 and 527 +/- 11 Myr, which are within error of the zircon ages but may reflect a lower blocking temperature. High-Th monazite rims with younger mean ages of 518 +/- 3 and 512 +/- 13 Myr occur around low-Th cores in both samples, and were precipitated from hydrous fluids released during the crystallization of residual melts. These magmatic fluids were channelled along the retrograde foliation present in both samples. All mineral assemblages and fabrics preserved in the metasediments reflect intense Pan-African metamorphism and deformation, associated with high degrees of partial melting and significant vertical displacements of the crust. Continental reconstructions assuming limited Pan-African tectonism in East Antarctica should be reassessed in the light of these new data.