Australia: The Land Where Time Began

A biography of the Australian continent 

West Australian Cratonic Assemblage (WAC)

In the WAC there are 3 terranes that are geologically distinct, that are inferred to have assembled by about 1.8 Ga. A microcontinent of Late Archaean-Palaeoproterozoic age is represented by the Gascoyne Complex, the microcontinent joining to the northern margin of the Yilgarn Craton, of Archaean age, along the Glenburgh Orogen, from 2.0-1.96 Ga (Sheppard & Occhipinti, 2000). The temporal and spatial distribution of granitoids have been interpreted as indicating north-dipping subduction followed by collision (Sheppard et al., 1996b). It was suggested (Myers, 1989) that the Trillbar Complex and the Narracoota Volcanics, thrust sheets of deformed, metamorphic mafic and ultramafic plutonic and volcanic rocks, transported from the north onto the Yilgarn Craton, represent parts of a volcanic arc that was obducted.

Based on magmatic and structural observations it was suggested that a N-S oblique convergence consumed an ocean basin between the Yilgarn and Pilbara Cratons, both of Archaean age, during the Capricorn Orogeny 1.83-1.78 Ma (Tyler & Thorne, 1990) and after about 1.62 Ga (Nelson, 1998) to accommodate sediments of the Bangemall Basin.

Sources & Further reading

1. Wingate, Michael T.D. & Evans, A.D., ed. Palaeomagnetic constraints on the Proterozoic evolution of Australia, Geological Society Special Publication 206