Structural and metamorphic evolution of the Mertz Shear Zone (East Antarctic Craton, George V Land): implications for Australia/Antarctica correlations and East Antarctic Craton/Ross orogen relationships

Field data from the coastal outcrops of the East Antarctic Craton in George V Land show the occurrence of a prominent mylonitic zone (the "Mertz Shear Zone", MSZ), with steeply dipping c. NNW-SSE oriented foliation planes and shear sense indicators indicating dextral sense of ductile shear. This paper focuses on the reconstruction of the complex structural and metamorphic evolution of this mylonitic zone which affects dominant enderbitic orthogneiss and minor sillimanite-garnet felsic granulite, variably retrogressed mafic granulites and amphibolites. Deformational fabrics include a series of progressive and overprinting shear structures, which developed during different metamorphic conditions (from early medium-pressure granulite grade to lower amphibolite and greenschist facies grade) but all with similar kinematics (dextral shearing). The MSZ marks the boundary zone between two domains with different lithological assemblages, age and metamorphic evolution. A low-pressure/high-temperature metamorphic event is documented in the area between Mertz and Ninnis Glaciers (Eastern Domain), which includes c. 500 Ma granitoids. In contrast, medium-pressure granulite-grade conditions are recorded in the rock units along the western margin of the Mertz Glacier (Western Domain), where a complex Late Archean to Palaeoproteozoic evolution is documented, apparently without evidence of c. 500 Ma orogenic tectonic or thermal reactivation. Comparison with the coastal region of southern Australia (Eyre Peninsula) indicates a probable correlation between the ductile MSZ and the c. 1.7 Ga Kalinjala Mylonite Zone within the Gawler Craton in South Australia. In this context, the MSZ and the proposed subdivision of the basement in George V Land have significant potential to contribute further data for both Gondwana and Rodinia reconstructions.