MAJOR STRUCTURAL ELEMENTS ALONG THE SOUTHERN CONTINUATION OF THE C. 640-500 MA EAST AFRICAN/ANTARCTIC OROGEN AND SIGNIFICANCE FOR RECONSTRUCTIONS IN RODINIA

A comparison of geological, geochronological and aerogeophyscial data in Dronning Maud Land (East Antarctica) highlight a number of important structural discontinuities, that were probably significant elements during the amalgamation of Gondwana. In Dronning Maud Land an Archean cratonic fragment, the Grunehogna craton, is exposed, that is rimmed by the c. 1.1 Ga Maud Belt. The Maud Belt is characterised by high-amplitude, elongate magnetic anomalies, that are parallel to the craton margin and coincide with craton-parallel shear zones. These anomalies can be correlated with similar anomalies in the Mesoproterozoic Natal Metamorphic Province of southern Africa, to which this part of East Antarctica was attached during the Mesoproterozoic. In Dronning Maud Land, these elongate anomalies terminate sharply at the Heimefront Shear Zone in western Dronning Maud Land. This dextral transpression zone coincides with Grenville-age Ar-Ar and K-Ar cooling ages to the W and Pan-African cooling ages to the E. The dextral sense of shear of this major shear zone contrasts with the overall sinistral transpressional character of the East African/Antarctic Orogen. East of the Heimefront shear zone, the basement has been pervasively reworked, and the degree of reworking and the grade of metamorphism increases E-wards. Since on either side of the Heimefront Shear Zone Grenville-age rocks are exposed, this structure is interpreted as the orogenic front of the southern continuation of the East African Orogen into East Antarctica. It is unlikely that this structure represents a suture. Laterally, the East African/Antarctic Orogen in Antarctica probably terminates in an escape tectonic regime, similar to the present situation in SE Asia. Lateral extrusion was associated with large transpressional shear zones such as the Heimefront Shear Zone. These shear zones were reactivated during Gondwana break-up and resulted in a characteristic microplate pattern within the Natal embayment during break-up. The molasse of the East African/Antarctic Orogen is preserved in shear zone bound pull-apart basins in e.g. SE Africa (Natal Group) and western Dronning Maud Land. For any Mesoproterozoic continent reconstruction, it is important to fully restore this Late Neoproterozoic/Early Paleozoic escape tectonics.