Neoproterozoic structural slices in the Ross Orogen, Skelton Glacier area, South Victoria Land, Antarctica

Abstract

Abstract In the Skelton Glacier area, metasedimentary basement of the Ross Orogen comprises nine structurally and lithologically distinct fault‐bounded crustal slices containing varying proportions of limestone, greywacke, argillite, conglomerate, calc‐silicate, basaltic and felsic igneous rocks, and migmatite. Unlike metasediments elsewhere in South Victoria Land, primary sedimentary features are locally preserved in some of the slices. The various slices are characterised by greenschist to upper amphibolite facies metamorphic assemblages with the presence of andalusite and cordierite indicating relatively low pressure conditions. Deformation within the slices is commonly inhomogeneous, most sequences are transposed, and lithologic contacts are generally tectonic. Multiple folding characterises the most ductile lithologies. The original name of Skelton Group is retained, but the extent of deformation precludes lithostratigraphic mapping, and the formal lithostratigraphic nomenclature previously applied is abandoned. The range of metamorphic facies implies several kilometres or more of offset along structures bounding the slices, and assembly of the various slices is Neoproterozoic, preceding 551 ± 4 Ma igneous intrusion. This complex history of deformation and metamorphism represents the earliest stage of orogenic activity in South Victoria Land and contrasts with rocks of the Walcott and Dry Valleys areas to the north, where the structural and metamorphic history is 20–50 m.y. younger.