Australia: The Land Where Time Began

A biography of the Australian continent 

Archaean Crust formation in Western Australia – Secular Change Recorded

According to Yuan, controversy remains concerning the mechanisms of formation of continental crust in the Archaean. The competing mechanisms for the formation of continental crust are accumulation by horizontal accretion, as in modern subduction zones, or by vertical accretion above upwelling zones in the upper mantle. A change in the characteristics of continental crust at the transition from the Archaean to the Proterozoic suggests continental crust did not form in subduction zones before the late Achaean, at the earliest. In this study seismic receiver function data was used to analyse the bulk properties of continental crust in Western Australia, which had formed and stabilised over a period of 1 Gyr during the Archaean. Yuan found that the bulk seismic properties of the crust clustered spatially, similar clusters being confined within the boundaries of tectonic terranes. Yuan demonstrated that plume and subduction processes may have both had as role in the formation of the crust throughout the Archaean by the use of local Archaean crustal growth models. A trend was revealed by correlating crustal age and bulk seismic properties of the crust: the crust thickened gradually from about 3.5 Ga to the end of the Archaean and its composition simultaneously became more evolved. It is proposed by Yuan that the transition between crust that had been formed dominantly by mantle plumes to crust that was formed by subduction processes is reflected in this trend, the transition possibly reflecting secular cooling of the mantle.

Sources & Further reading

1. Yuan, H. (2015). "Secular change in Archaean crust formation recorded in Western Australia." Nature Geosci 8(10): 808-813.