The metamorphic evolution of granulites at Fyfe Hills; implications for Archaean crustal thickness in Enderby Land, Antarctica

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Abstract
Granulites at Fyfe Hills in Enderby Land, Antarctica, crystallized at temperatures in excess of 850°C, and possibly as high as 1000°C, and at pressures of 8‐10kbar during the mid to late Archaean. A number of features, including repeated retrograde metamorphism at 5.5‐8kbar, retrograde reaction textures, and rimward zoning in pressure sensitive systems, suggest that following peak metamorphism the granulites stabilized at a depth of 18‐26 km. After stabilization, the granulites cooled near‐isobarically to temperatures of 600‐700°C. Assuming a total crustal thickness of 35‐40 km during this late Archaean interval of isobaric cooling, the peak metamorphic crustal thickness is estimated at 35‐56 km. This estimate is significantly less than the 60‐70 km obtained by summing the depths of the present levels of exposure (26‐34 km) and the thickness of the crust presently beneath Fyfe Hills (approxi‐mately 35km) and is, therefore, consistent with independent evidence for extensive post‐Archaean thickening of the Enderby Land crust.