Gascoyne Complex

The Gascoyne Complex is a terrane of Proterozoic granite and metamorphic rock in the central-western part of Western Australia. The complex outcrops at the exposed western end of the Capricorn Orogen, a 1,000 km-long arcuate belt of folded, faulted and metamorphosed rocks between two Archean cratons; the Pilbara craton to the north and the Yilgarn craton to the south. The Gascoyne Complex is thought to record the collision of these two different Archean continental fragments during the Capricorn Orogeny at 1830–1780 Ma.

The Gascoyne Complex is separated from the Yilgarn Craton to the south by a major fault, the Errabiddy Shear Zone. To the east and northeast rocks of the complex are overlain unconformably by fine-grained Mesoproterozoic sedimentary rocks of the Edmund Basin and Collier Basin (formerly known as the Bangemall Basin). Several inliers of granite within these sedimentary basins also belong to the Gascoyne Complex. To the west, the Gascoyne Complex is overlain unconformably by sedimentary rocks of the Phanerozoic Carnarvon Basin. To the north, schist of the Gascoyne Complex probably pass with decreasing intensity of metamorphism into metamorphosed sedimentary rocks of the upper Wyloo Group.

The Gascoyne Complex is divided into two parts, the 1840–1620 Ma northern and central Gascoyne Complex, and the 2005–1970 Ma Glenburgh Terrane in the southern Gascoyne Complex. The two are separated by a major east-southeast trending fault, the Chalba Shear Zone. Rocks of the Glenburgh Terrane do not outcrop at surface north of the Chalba Shear Zone, but it is unclear as to whether or not rocks of this terrane floor all or part of the central and northern Gascoyne Complex.

The Gascoyne Complex has been shaped by four orogenies, the most important and widespread of which were the 1830–1780 Ma Capricorn Orogeny and the 1680–1620 Ma Mangaroon Orogeny. Both of these orogenies were marked by extensive folding, faulting and metamorphism, and were accompanied by the intrusion of large volumes of granite referred to as supersuites. The effects of the oldest orogeny, the 2005–1960 Ma Glenburgh Orogeny, although known only from the southern end of the complex, reflect a period of substantial granite magmatism and intense deformation and metamorphism. The Neoproterozoic Edmundian Orogeny mainly consists of the reactivation of earlier formed faults in the Gascoyne Complex, along with folding and faulting of the overlying Edmund and Collier basins.

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