McInnes, Brent I.A.
1John de Laeter Centre, Curtin University, Perth, Australia
The field of thermochronology in Australia has seen a significant increase in both capability and capacity development over the last decade. New labs have sprung up at University of Adelaide, the University of Queensland and Curtin University, which augment the University of Melbourne lab which has been a research powerhouse for almost half a century. These lab developments are one of many positive outcomes of informal meetings organised by geochemistry labs around the country via TANG3O (Thermochronology and Noble Gas Geochronology and Geochemistry Organisation).
Most labs now take an integrative approach using multiple radiometric dating techniques (e.g., U-Pb, Ar-Ar, U-He, fission-track) to generate geothermochronology data sets which provide a complete cooling history for any given rock sample. Repeating this process for multiple samples at scale allows researchers to detect differences in thermal history models that reflect major tectonic events in crustal evolution (e.g., continental breakup and collision, mountain-building and basin formation). Computational inversion of geothermochronology datasets are also becoming more sophisticated and allow the 4D thermal evolution of the crust to be imaged, providing a more detailed understanding of tectonic processes as well as predictive capability in the search for mineral and energy resources.
Another promising development is the increasing collaboration between research labs and geological surveys across Australia to address significant geoscience questions, such as: (1) mapping out thermal events across the continent (e.g., National Argon Map project led by Geoscience Australia), (2) demarcation of the end of orogenic events (Hall et al., 2016; Quentin de Gromard et al., 2020), and (3) regolith geochronology (Wells et al., 2019). Continued cooperation will lead to the training of a cadre of young geoscientists skilled in being able to provide a “biography” of a geological unit rather than just its “birth date”.
Challenges remain however in understanding the crystal chemistry factors that produce inaccurate or irreproducible thermochronology ages in Archean and Proterozoic lithologies. The in situ U-Th/Pb-He microanalysis approach (Danisik et al., 2017), which generates grain-scale zircon He maps and quantifies intragrain He distribution, can be used by researchers to exclude problem areas in grains with anomalous He concentrations due to crystal defects or inclusions. The potential adoption of in situ microanalysis in thermochronology can be viewed similarly to the paradigm shift experienced by the geoscience community when SHRIMP became available in the 1990’s, an event which led to orders of magnitude increase in zircon U-Pb data production and fundamental changes to the design of geological maps and our understanding of the planet.
Danišík, M et al (2017) Seeing is believing: Visualization of He distribution in zircon and implications for thermal history reconstruction on single crystals. Science Advances 3:2, e1601121. DOI: 10.1126/sciadv.1601121.
Hall, JW et al (2016) Exhumation history of the Peake and Denison Inliers: insights from low-temperature thermochronology. AJES 63:7, 805-820. DOI: 10.1080/08120099.2016.1253615
Quentin de Gromard, R et al (2019) When will it end? Long-lived intracontinental reactivation in central Australia. Geoscience Frontiers, 10, 149-164. DOI: 10.1016/j.gsf.2018.09.003
Wells, MA et al (2019) (U-Th)/He-dating of ferruginous duricrust: Insight into laterite formation at Boddington, WA. Chemical Geology 522, 148-161. DOI: 10.1016/j.chemgeo.2019.05.030
Professor Brent McInnes is a Research Professor at Curtin University and Director of the John De Laeter Centre, WA. Previous to this he was a Chief Research Scientist at CSIRO. Educated in Canada and trained at Caltech, he has 28 years of experience in the geoscience and resources research sector.