Fraser, Geoff1, Waltenberg, Kathryn1, Jones, Sharon1, Huston, David1, Champion, David1, Bodorkos, Simon1
1Geoscience Australia, Canberra, Australia
Australia has been, and continues to be, a leader in isotope geochronology and geochemistry. This has included fundamental contributions to instrumentation, method development and geological applications. While new isotopic data is being produced with ever increasing pace and diversity, there is also a rich legacy of existing high-quality age and isotopic data, most of which have been dispersed across a multitude of journal papers, reports and theses. Where compilations of isotopic data exist, they tend to have been undertaken at variable geographic scale, with variable purpose, format, styles, levels of detail and degree of completeness. Consequently, it has been difficult to visualise or interrogate the collective value of age and isotopic data at continental-scale. Contrast this situation with the almost ubiquitious use of national-scale geophysical data coverages, such as magnetic and gravity compilations. Age and isotopic patterns at continental scale can provide intriguing insights into the temporal and chemical evolution of the continent, and an opportunity to add additional geological meaning to such geophysical coverages.
As national custodian of geoscience data, Geoscience Australia has addressed this challenge by developing an Isotopic Atlas of Australia, which so-far consists of national-scale coverages of five widely-used age and isotopic data-types, as follows:
- Sm-Nd whole-rock analyses of granites and felsic volcanics
- Lu-Hf analyses of zircon
- Pb-Pb of ore-related minerals – primarily galena and pyrite
- U-Pb mineral ages from magmatic, metamorphic and sedimentary rocks (typically zircon but also including monazite, titanite, baddleyite…)
- K-Ar and 40Ar-39Ar analyses of minerals and whole rocks.
Several of these isotopic coverages are now freely available as web-services for use and download from the GA Portal (www.portal.ga.gov.au). While there is more legacy data to be added, and a never-ending stream of new data constantly emerging, the provision of these national coverages with consistent classification and attribution provides a range of benefits:
- it vastly reduces duplication of effort in compiling bespoke datasets for specific regions or use-cases
- data density is sufficient to reveal meaningful temporal and spatial patterns
- a guide to the existence and source of data in areas of interest, and of major data gaps to be addressed in future work
- facilitates production of thematic maps from subsets of data. For example, a magmatic age map, or K-Ar mica cooling age map
- sample metadata such as lithology and stratigraphic unit is associated with each isotopic result, allowing for further filtering, subsetting and interpretation.
The GA Portal also contains a great diversity of other geological, geophysical and geographic coverages. This provides the opportunity to conveniently overlay age and isotopic patterns with geological maps, major structural and province boundaries, crustal and lithospheric thickness, seismic velocity images, electrical conductivity maps, and many more. There is much to be explored in these comparisons and correlations.
The Isotopic Atlas of Australia will continue to develop via the addition of both new and legacy data to existing coverages, and by the addition of new data coverages from a wider range of isotopic systems and a wider range of geological sample media (e.g. soil, regolith and groundwater).
Kathryn Waltenberg is a geochronologist and isotope geochemist, with experience in diverse applications of the Ar-Ar, U-Pb and Lu-Hf isotopic systems. Kathryn has worked at Geoscience Australia since 2013, where she is currently Activity Leader for Age and Isotopic Mapping.