Australia: The Land Where Time Began

A biography of the Australian continent 

Mesoproterozoic Plume-Modified Orogenesis in Eastern Precambrian Australia

Very large volumes of magma that was derived from the mantle were added to the crust of the Musgrave region, central Australia more than 1,090 Ma to more than 1,040 Ma during the Giles Event. The Mantamaru Intrusion, one of the largest mafic intrusions in the world, was included in this event, and about 1,075 Ma the Warakurna Large Igneous Province formed, which spread intrusions of dolerite across about 1.5 million km² of western and central Australia. Also included was one of the most voluminous additions of juvenile felsic material to the crust of the Earth, with the development of one of the longest-lived rhyolite centres, which included the Talbot Supervolcano. It has been suggested previously that the event resulted from a deep mantle plume, but this is suggested by Betts et al. to not be able to adequately account for the duration of mantle derived magmatism that lasted for more than 50 Myr, or for isolated localities such as the Talbot Sub-basin that preserve the entire magmatic record, with no regional age progressive spatial trend that is discernible. The Musgrave region experienced high to ultrahigh crustal temperatures for at least 100 Myr prior to the Giles Event, possibly as an ultrahot orogen that formed from a backarc dating to about 1,300 Ma. A significant mantle-derived component was also involved in granitic magmatism that occurred prior to the Giles Event and was accompanied by ultra-high temperature, above 1,000^oC, metamorphism in a mid-crustal location that reflected a thin, weak lithosphere. This magmatism also led to a mid-crustal (about 25 km deep) layer that was greatly enriched with radiogenic heat producing elements that augmented strongly the crustal geotherms that was already extreme over a long period. Betts et al. suggest that when this regional Musgrave thermal anomaly was displaced it may have triggered the Giles Event, and again significantly destabilised, along the Mundrabilla Shear Zone – a continental scale structure, that juxtaposed the Musgrave Province against the easterly extension of the Capricorn Orogen where preexisting orogen-scale structures were in extension. The magmas that produced the Warakurna Large Igneous Province were funnelled by these orogen-scale structures and the intersection of the Musgrave Thermal Anomaly and the Mundrabilla Shear Zone was the location of the Talbot supervolcano. Betts et al. suggest the Giles Event was likely to have been the product of intraplate tectonic processes that involved a thermal prehistory that was anomalous and prolonged, a magma-focussing lithospheric architecture, and tectonic movements on a large scale.

Sources & Further reading

1. Betts, P. G., D. Giles, J. Foden, B. F. Schaefer, G. Mark, M. J. Pankhurst, C. J. Forbes, H. A. Williams, N. C. Chalmers and Q. Hills (2009). "Mesoproterozoic plume-modified orogenesis in eastern Precambrian Australia." Tectonics 28(3): n/a-n/a.