Schirmacher Oasis as an Extension of the Neoproterozoic East African Orogen into Antarctica: New Sm‐Nd Isochron Age Constraints

This is the authors' abstract. We don't add key points for this paper.

The chronology of tectonometamorphic events in granulite terranes of Dronning Maud Land, East Antarctica, is relevant to the controversy regarding the correlation of the Neoproterozoic East African Orogen into Antarctica. The Schirmacher Oasis in the northern Dronning Maud Land preserves medium‐pressure (8 kbar, 800°C) granulite assemblages whose evolution has been proposed to involve a major and regionally pervasive tectonometamorphic cycle (D2/M2). The trajectory of the retrograde P‐T segment for this cycle shows an early stage of near‐isothermal decompression, succeeded by prominent near‐isobaric cooling within the field of sillimanite stability. A suite of syn‐D2 enderbitic orthogneisses within metapelite and quartzofeldspathic gneisses yields a whole‐rock Sm‐Nd isochron age at 616± 52 Ma (2σ) and an initial Nd isotopic ratio of 0.511844± 50 (ε Nd\,≈ 0 ). A mineral isochron defined mainly by the coronal garnet in one of these samples also gives very similar results (632± 8 Ma, 0.511836± 14 , ε Nd\,≈ 0 ), interpreted as the age for the near‐isobaric cooling stage of the pervasive D2/M2 event in the Schirmacher region. A distinctly younger whole‐rock garnet Sm‐Nd isochron age at 554± 16 Ma for sheared enderbitic gneiss dates widespread shearing, granite intrusion, and retrogression at amphibolite‐facies conditions throughout the Schirmacher region because of a later thermal and deformation event (D3/M3). From similarities with the ages and geologic setting of klippe in the Lurio Belt Foreland, the Schirmacher Oasis is interpreted as part of a klippen of the Lurio Belt of southeast Mozambique and can be considered as an extension of the East African Orogen into Antarctica.