Three billion years of granite magmatism: Palaeo-Archaean to Permian granites of Australia

• Reference
• Summary
• Download the full presentation
• Further information

Reference

Recommended citation: Champion, D.C. & Smithies, R.H., 2007. Three billion years of granite magmatism: Palaeoarchaean to Permian granites of Australia. Sixth International Hutton Symposium, Origin of granites and related rocks, University of Stellenbosch, South Africa, 2-6 July, 2007.

Summary

This invited keynote address was presented at the Sixth International Hutton Symposium, Origin of granites and related rocks, held at the University of Stellenbosch, South Africa, on 2-6 July, 2007.

Felsic magmatism in Australia ranges in age from Paleoarchaean to Mesozoic. Extensive episodes occurred in the Palaeo-, Meso-, and Neoarchaean, Palaeo- and Mesoproterozoic, and Silurian-Devonian, and Carboniferous-Permian.

Like the Archaean elsewhere, the Archaean Pilbara and Yilgarn Cratons in Western Australia are dominated by sodic felsic granites of the tonalite-trondhjemite-granodiorite (TTG) suite. This earliest magmatism reflects melting of a basaltic protolith, mostly at high pressures, either within subducted slabs or thickened crust. Sodic granites also form a persistent component of Proterozoic and Palaeozoic magmatism in Australia although in no specific period are they found in the same abundance as for the Archaean.

The other dominant magmatic series in the Australian Archaean are potassic granites. These mostly postdate and largely reflect crustal reworking of the sodic granites. An important sub-class are those with high-silica and often moderately to strongly differentiated compositions. These first appear in the Mesoarchaean, but are most extensive in the Neoarchaean of the Yilgarn Craton (>100,000 square kilometres within a 25 million year period). Similar high-silica rocks occur in both the Proterozoic and Palaeozoic. Tectonic environments for these rocks are not well understood. One feature of these rocks is elevated thorium (Th) and uranium (U) contents.

A wide variety of other (intermediate-) felsic magmatic rocks are present in the Archaean to Palaeozoic geological provinces of Australia. These include: high-Mg diorite as well as components of the basalt-andesite-dacite-rhyolite series (locally with boninite-like rocks), which provide strong evidence for modern-style arc-related processes as far back as the Mesoarchaean; peralkaline rocks such as syenites (as old as Mesoarchaean); and high temperature, Fe- and HFSE-rich rocks, i.e., A-types (as old as Paleoarchaean). Perhaps the most significant secular change in Australia is for S-type magmatism, which is rare in the Archaean, minor in the Proterozoic, and common in the Palaeozoic.

The Australian record shows that, in general, none of the felsic magmatic series are confined to or excluded from any particular time, but rather it is the relative proportions of such rocks which vary with time. Although similar chemistries could reflect similar responses to different processes, the simplest interpretation is that they reflect similar processes. A corollary is that a similar range of tectonic processes has operated from the Paleoarchaean to now, but the dominance of particular processes has changed. This conclusion is balanced against observed subtle changes in chemistry which may indicate secular changes in tectonic processes, e.g., slab melting (TTGs) to slab dehydration (calc-alkaline rocks).

[back to top]

Download

Three billion years of granite magmatism: Palaeo-Archaean to Permian granites of Australia

• Part 1 PDF 3MB
• Part 2 PDF 5MB
• Part 3 PDF 7MB

Further information

For further information please email David Champion, or phone +61 2 6249 9215.