Thursday, 30 August 2007
4.PS-95
Sm-Nd and U-Pb isotopic constraints for Late Neoproterozoic crustal evolution from granulites of the Schirmacher Oasis, East Antarctica: geodynamic development coeval with the East African Orogeny
V. Ravikant1, Jorge H. Laux2, and Marcio M. Pimentel2. (1) Geochronology and Isotope Geology Division, Geological Survey of India, 15 A&B Kyd Street, Kolkata 700016, India, (2) Universidade de Brasilia, Laboratorio de Geocronologia, Instituto de Geociencias, Brasilia DF-70910, Brazil
Formation of Neoproterozic granulites, remnants of which are exposed in coastal Antarctica and SE Africa , is controversial; dating of high-grade metamorphism was performed to correlate these granulite-facies remnants. The results of this Sm-Nd garnet and U-Pb monazite and titanite geochronological study from metasedimentary rocks, melanocratic gabbronorite and websterite, indicate peak granulite-facies metamorphism to have occurred between 660 and 630 Ma followed by cooling lasting between 630-580 Ma. The ages are older than those determined earlier on zircon at ~ 624-626 to 615 Ma. This supports a short time span for the medium-pressure granulite-facies metamorphism by increased geothermal gradient due to crustal stacking and inflation, due to intrusion of quartz-diorite and tonalite (protoliths to the enderbitic gneiss), at an active continental margin. A collision between the ~1.1 Ga orogenic Maud Belt with a northerly Mesoproterozoic arc-defined Lurio-Nampula block was responsible for formation of this Neoproterozic orogen and the Kalahari peninsula.