East Antarctic crustal evolution: Geological constraints and modelling in western Dronning Maud Land

Two geological provinces of western Dronning Maud Land provide constraints which allow preliminary modelling of crustal evolution in this part of East Antarctica. The Grunehogna province comprises a 3000 Ma granitic basement overlain by a 1000 Ma sequence of sedimentary and volcanic 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-alkaline metavolcanic rocks suggesting a volcanic are environment; (ii) further to the east and southeast are granulite facies para- and ortho-gneisses compatible with a retro-arc marginal basin heritage. Both assemblages were intruded by Proterozoic and lower Phanerozoic granitoids and provide evidence of two distinct major events in the orogenic history. In the eastern assemblage, the first event (1200-900 Ma) involved metamorphism with initial high pressures (12-15 kbar, 750 degrees C) followed by decompression and thermal relaxation (8 kbar, 850 degrees C), a path attributed to continental collision with deep burial of a marginal basin characterised by an elevated geotherm. The second event (similar to 500 Ma), also under medium- to high-grade metamorphic conditions (similar to 600 degrees C, 5-6 kbar), caused tectonic inversion of the metamorphic profile by thrusting followed by rapid uplift and exhumation. Tectonothermal overprinting of the Maud Belt and folding of the 1000 Ma supracrustal sequence near boundaries between the cratonic 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 this area as a portion of the Kalahari Craton detached during Gondwana break-up. Similar overprinting of the Proterozoic belts in Africa, such as the Mozambique belt, suggests that these zones of crustal disequilibrium were the loci of repeated continental break-up and convergence.