The Relationship Between Crustal Architecture, Deformation, and Magmatism in the Coompana Province, Australia

Abstract

The Coompana Province, located between the three cratonic blocks of Australia, is significant for understanding the Proterozoic assembly of the continent. However, the basement rocks are completely covered and poorly understood, and as a result reconstructions are poorly constrained. Recent collection of detailed geophysical data sets and a stratigraphic drilling campaign in the eastern Coompana Province is used to understand the crustal architecture and tectonomagmatic history of the region. A north to northeast trending grain represents a series of amalgamated 1618–1526 Ma tectonic belts between the Western and South Australian cratons. These belts are cut by a northeast trending, shear-bounded corridor of thinned crust, intruded by voluminous circa 1150–1140 Ma granite plutons. The new data indicate two main stages of deformation between circa 1200 and 1140 Ma. Circa 1200–1170 Ma east-west extension was pervasive, causing widespread partial melting, shallowly dipping layering, recumbent folding, and minor shoshonitic magmatism. Circa 1160–1140 Ma deformation was partitioned into the northeast trending corridor, which focused transfer and emplacement of voluminous A-type magmas. The two stages represent a switch from pervasive to localized deformation, with accompanying changes in magmatic style. Early pervasive extension caused progressive melt extraction, producing small sheets. Subsequent shearing locally promoted melt reorganization in the lower and middle crust. This caused local changes in rock strength with the continued partitioning of deformation into the oblique corridor. The crustal-scale structures disrupted the lower crustal MASH zones, mobilizing and focusing the voluminous magmatism.