Glenelg River Complex

Abstract

Low-grade regionally metamorphosed slates, phyllites and metagreywackes, and higher-grade low-pressure-high-temperature metamorphic rocks in the Glenelg River Complex are structurally, lithologically and sedimentologically similar to Cambrian sequences in the South Australian Kanmantoo Group. Peak metamorphic conditions (650°C; 3-4 kbar) occurred during the D2 deformation and coincided with synkinematic intrusion of Cambro-Ordovician I- and S-type granites and pegmatite. D2 folds are non-cylindrical on all scales, verge westwards towards the Australian craton, and include tight to isoclinal NW-trending structures which have been variably rotated into parallelism with the D2 extension direction. These folds and their accompanying high-grade metamorphism post-date low-grade regional metamorphism and are inferred to have developed during west-vergent thrust faulting and crustal thickening in common with other parts of the Delamerian Fold Belt. To the east, the Glenelg River Complex is faulted against (? Cambrian) slates and an unconformably overlying sequence of late Silurian-earliest Devonian siliciclastic sediments (Grampians Group) which have been intruded by 400-Ma I-type granites. This fault marks the eastern limit of Delamerian granite magmatism in Victoria and possibly represents the boundary between the Lachlan and Delamerian fold belts. An analogous crustal boundary (Lanterman Fault Zone) identified in Antarctica (northern Victoria Land) provides an important constraint on plate tectonic reconstructions of the southwest Pacific sector of Gondwana. Show more