Role of geochronology in our present-day understanding of the Proterozoic: an Australian perspective

Abstract

Geochronology has proven pivotal to our present-day understanding of the dynamic processes that have shaped the Earth. The proliferation of high-precision geochronology worldwide in the last 15 years, in particular that generated by sensitive high-resolution ion microprobe (SHRIMP), has revolutionised the geological community's view of the Proterozoic Eon, and the implicit assumptions that form the basis of most work conducted on rocks of that age. Although most of this dating has concentrated on U–Pb zircon ages in felsic rocks, an impressive record of Proterozoic crust-forming events and high-grade tectonic reworking has been identified. In some instances, the dating has also defined the duration of orogenic activity. Our present-day understanding is that: (i) many Proterozoic orogens mark ancient collision zones, and as a corollary, plate tectonics has operated throughout the Proterozoic; (ii) Proterozoic orogens were commonly the sites of repeated reworking or reactivation; (iii) the Proterozoic saw the assembly and dispersal of at least two supercontinents; (iv) the Proterozoic was punctuated by the activity of numerous large igneous provinces; and (v) Proterozoic basin formation and evolution were driven largely by plate-tectonic processes. Although there are large areas yet to be dated, there is no reason to suggest that the processes identified there will be any different. The primary question has evolved from ‘Did plate tectonics operate?’ to ‘What form did plate tectonics take?’ One of our major challenges is to extend the geochronological framework of the Proterozoic by routinely dating other uranium-bearing accessory phases, following the successful application of zircon geochronology.

Key Words:

• Australia
• geochronology
• monazite
• Proterozoic
• SHRIMP
• tectonics
• uranium–lead dating
• zircon

Acknowledgements

We thank John De Laeter and David Nelson for the invitation to write this paper and for their encouragement, Michael Wingate for two of the figures, and Simon Johnson for his advice. We also thank Keith Sircombe and an anonymous reviewer for their comments. SS, SB and IMT publish with permission of the Executive Director, Geological Survey of Western Australia.