Timing of Grenville-age vs. Pan-African medium- to high grade metamorphism in western Dronning Maud Land (East Antarctica) and significance for correlations in Rodinia and Gondwana

Abstract

Heimefrontfjella in western Dronning Maud Land, East Antarctica, is part of the c. 1.1 Ga Namaqua-Natal-Maud Belt. It is situated at an important location, both for Rodinia reconstructions and at the western orogenic front of the Late Neoproterozoic/Early Palaeozoic East African/Antarctic Orogen. Six basement samples help to precisely date the Grenville-age metamorphism between c. 1090 and 1060 Ma. These dates indicate that palaeomagnetic data from the Coats Land Block to the south of the Maud Belt cannot be taken to support the contiguity of the Coats Land/Maud/Grunehogna continental fragment and Kalahari during Late Mesoproterozoic times. A comparison of aeromagnetic data and crustal provinces indicates that the Coats Land basement is likely to be composed of pre-Mesoproterozoic basement that was differentially reworked at c. 500 Ma within the East African/Antarctic Orogen. The western orogenic front of the East African/Antarctic Orogen is exposed as the Heimefront Shear Zone. Zircons from this shear zone show a thin, low-U, reaction zone that probably resulted from mylonitisation at amphibolite facies conditions. The rims were too thin to be analysed. However, only a few kilometres to the E of the shear zone, c. 500 Ma Pan-African zircon overgrowth is present, clearly indicating intense Late Neoproterozoic/Early Palaeozoic reworking of the Grenville-age basement and allowing the direct dating of this younger overprint. High grade reworking must have been followed by rapid cooling, as shown by a number of c. 500 Ma K-Ar and Ar-Ar hornblende and mica ages. Whereas the western orogenic front of the East African/Antarctic Orogen is exposed as the Heimefront Shear Zone, the eastern orogenic front might be represented by the Otter Highland Thrust in the Shackleton Range, with variably reworked crust up to granulite facies in between these two structural discontinuities.