Geology and structure of Depot Peak, MacRobertson Land. More evidence for the continuous extent of the 1000 Ma event of East Antarctica

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Abstract
The 1000 Ma event of East Antarctica is a granulite facies metamorphic event that affected rocks underlying more than 1000 km of the Antarctic coastline between 50°E and 70°E. The limits of the belt are defined by isotopic dating but attempts to define the belt on metamorphic grounds are sparse. Depot Peak provides an important link for determining the history of this belt as it is the only outcrop linking the Prince Charles Mountains to the Framnes Mountains and the western parts of the Rayner Complex. Much of the Prince Charles Mountains are also 1000 Ma old but much of their metamorphic history is yet to be established. The rocks at Depot Peak are garnet and cordierite‐bearing gneisses of low pressure granulite facies that were intruded by a large sheet of garnet granite prior to metamorphism and deformation. They experienced two deformation phases, D1 and D2, and they record two different metamorphic events around 560 MPa, 700°C (M1) and 510 MPa, 600°C (M2). It is difficult to demonstrate to what extent this fragmental record actually reflects the metamorphic peak conditions or even a retrograde pressure‐temperature path. Nevertheless, the metamorphic record is very similar to that of many other granulite rocks from the 1000 Ma belt and it appears reasonable to assume that it is the consequence of the same metamorphic processes in all areas. This paper presents further evidence for the two dimensional extent of the belt, a feature that is difficult to reconcile with an interpretation based on a plate tectonic context. It is more likely that the metamorphic peak record for Depot Peak reflects a thermal buffering phase in the cooling history, rather than the absolute metamorphic peak.

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