Mafic dykes in the Rauer Islands and Vestfold Hills (East Antarctica): A chemical and Nd isotopic comparison

Abstract

The Rauer Islands and neighbouring Vestfold Hills are intruded by numerous mafic dykes. In the latter area the dykes are basically not deformed, albeit metamorphosed in the southwestern part, whereas in the former they are strongly deformed and metamorphosed. In Scherbinina Island they intrude Archaean rocks and their ages are between ca. 2800 Ma and ca. 530 Ma, while in Efremova, Filla, and Hop islands they intrude Mesoproterozoic ca. 1150 Ma or ca. 1000 Ma orthogneiss and pre-date ca. 1000–950 Ma tectonism. A comparison and possible correlation between dykes in the Rauer Islands and the Vestfold Hills is a crucial point in the interpretation of the regional tectonic evolution. We present ICP-MS analyses of trace elements and Nd isotopic data for mafic dykes from Rauer Islands and Vestfold Hills. Two chemically distinct dyke groups are distinguished in the Rauer Islands: low-LILE group which was sampled from Scherbinina, Efremova and west Filla islands, and high-LILE group which was sampled only from Hop and central Filla islands. The low-LILE dykes were emplaced into ca. 1150 Ma orthogneisses and more ancient rocks, but were not found within ca. 1000 Ma orthogneisses, whereas the high-LILE dykes intrude ca. 1000 Ma orthogneiss, but were not found within Archaean rocks. The low-LILE group displays many chemical and Nd isotopic features in common with high-Fe mafic dykes in the Vestfold Hills, but the age uncertainties preclude a correlation. The formation of the high-LILE mafic dykes in the Rauer Islands indicates magmatism in late-orogenic environments at the end of the Rayner Orogeny.Our data argue against direct correlation between mafic dykes in Rauer Islands and Vestfold Hills, in spite of similar tholeiitic whole rock compositions. The Vestfold Hills dykes experienced cooling to the Sm–Nd systematic closure temperature by 790 Ma and subsequent shearing at ca 635 Ma (garnet – whole rock). Considering the data published elsewhere we interpret that the Vestfold and Rauer crustal blocks experienced shared tectonothermal histories since ca 950 Ma but may have been conjugated in the present positions only by the late Neoproterozoic due to horizontal transport along a major transcurrent shear zone.