Sinistral transpressional and extensional tectonics in Dronning Maud Land, East Antarctica, including the Sør Rondane Mountains

Abstract

In this paper we clarify the history of deformation in the Sør Rondane Mountains (SRMs), eastern Dronning Maud Land (DML), East Antarctica, and construct a form-line contour map of the metamorphic and plutonic rocks in order to comprehend their structural features and provide constraints on the collisional tectonics of East and West Gondwana. We divide the deformational history in the SRMs into 13 stages (D1–D13). The tectonic regime varied frequently from extension (D3–D4) to layer-normal compression and layer-parallel extension (D5), to compression (D6), extension (D7), sinistral transtension and sinistral strike-slip (D8), compression (D9–D11), and finally extension related to dextral shearing (D12–D13). D7 and D8 indicate major extensional tectonic activity in the southern part of the East African and Antarctic Orogen (EAAO) before the Pan-African compressional event, and after the c. 600Ma peak of metamorphism. The Pan-African compressional event resulted in the formation of upright folds with horizontal axes that curve along the coastline in central to eastern DML during the D9 deformation that took place between 600 and 560Ma. The coastline-parallel fold axes and subvertical axial-planes correspond to the X-axes and the XY-planes, respectively, of strain ellipsoids that were progressively rotated counterclockwise toward the central parts of a sinistral shear zone. Therefore, the curved fold axes and axial-planes suggest the EAAO acted as a zone of sinistral transpression during the collision of parts of East and West Gondwana. Around 560–550Ma, during D12, parallel dyke swarms of granitic pegmatite were intruded along normal faults under a regime of NNE–SSW horizontal extensional stress. The extensional paleo-stress and its related structures suggest dextral rather than sinistral shearing took place along the north-trending EAAO during this late Pan-African event. There is the possibility of a reversal of trans-orogen asymmetry from sinistral to dextral in the southern part of the EAAO. The dyke swarms are considered to have been the heralds of the voluminous 530–500Ma A-type granite intrusions in DML. At the same time, the Lützow–Holm Complex was under a non-extensional tectonic regime, and may have been situated in a different orogen from the EAAO.