EAST ANTARCTIC CRUSTAL EVOLUTION - GEOLOGICAL CONSTRAINTS AND MODELING IN WESTERN DRONNING-MAUD-LAND

Two geological provinces of western Dronning Maud Land provide constra ints which allow preliminary modelling of crustal evolution in this pa rt of East Antarctica. The Grunehogna province comprises a 3000 Ma gra nitic basement overlain by a 1000 Ma sequence of sedimentary and volca nic rocks which accumulated in a foreland basin. Juxtaposed with this cratonic province is the Mesoproterozoic Maud orogenic belt. The H.U, Sverdrupfjella portion of this belt consists of two lithostratigraphic assemblages: (i) adjacent to the suture are amphibolite facies calc-a lkaline metavolcanic rocks suggesting a volcanic are environment; (ii) further to the east and southeast are granulite facies para- and orth o-gneisses compatible with a retro-arc marginal basin heritage. Both a ssemblages were intruded by Proterozoic and lower Phanerozoic granitoi ds and provide evidence of two distinct major events in the orogenic h istory. In the eastern assemblage, the first event (1200-900 Ma) invol ved metamorphism with initial high pressures (12-15 kbar, 750 degrees C) followed by decompression and thermal relaxation (8 kbar, 850 degre es C), a path attributed to continental collision with deep burial of a marginal basin characterised by an elevated geotherm. The second eve nt (similar to 500 Ma), also under medium- to high-grade metamorphic c onditions (similar to 600 degrees C, 5-6 kbar), caused tectonic invers ion of the metamorphic profile by thrusting followed by rapid uplift a nd exhumation. Tectonothermal overprinting of the Maud Belt and foldin g of the 1000 Ma supracrustal sequence near boundaries between the cra tonic and orogenic terrains suggest that a Cambrian-Ordovician suture is close to (within?) the 1000 Ma belt. Geological correlation of the two Antarctic provinces with those in southeastern Africa identifies t his area as a portion of the Kalahari Craton detached during Gondwana break-up. Similar overprinting of the Proterozoic belts in Africa, suc h as the Mozambique belt, suggests that these zones of crustal disequi librium were the loci of repeated continental break-up and convergence .