research program 1
regolith geoscience
Geochronology and quantitative models of landscape evolution
Project Leader : Brad Pillans, Australian National University
Start date and duration: 01/07/03 – 30/06/08
Participants : Australian National University, external collaboration with University of Wollongong and Melbourne University
Brief project description :
To provide reliable numerical ages for regolith material, and to develop quantitative models of landscape evolution in regions which are important for mineral exploration and land management. Focus regions may include: Yilgarn Craton, Western NSW , Curnamona Province , Eucla margins and Northern Territory (especially Tanami region). Other focus regions may be recommended. Planned collaboration with Allan Chivas (stable isotopes; University of Wollongong ), Barry Kohn (fission-track; Melbourne University ) and Ken Fifield (cosmogenic nuclides, ANU).
Throughout the project we have focussed on dating weathering imprints in regolith using paleomagnetism, which has proved a cost-effective way dating oxidised regolith throughout Australia . Results show that there have been periods of enhanced oxidation and weathering extending back to Permo-Carboniferous times. Recently, multi-method approaches to regolith dating have been pioneered using K/Ar, U/Pb, (U-Th)/He and U-series methods in parallel with paleomagnetic dating. Opal, silcrete and iron oxides are being investigated as potential multi-method dating targets. Luminescence techniques have been used to measure rates of biological turnover in soils, and to establish the age of “parna” (aeolian dust) in a key section within the Lachlan Fold Belt, both leading to a better understanding of soil dynamics. Further work on dating of silcrete is being undertaken by Rainer Grun (Electron Spin Resonance) and Jim Dunlap (U-Th/He). Long term erosion rates in the Tanami region and the Harden area ( Murray-Darling Basin , NSW) are being measured using cosmogneic nuclides.
In 2007-08 we are concentrating on completing the dating program in the selected focus regions (above), working almost exclusively on samples already in-hand. James Hughes (ANU) will undertake an honours project, linked to the Salinity Program, in the Harden area, NSW, which will include collection of samples for luminescence, paleomagnetic and cosmogenic nuclide dating. Brad Pillans will undertake final field collection of paleomagnetic samples in the Yilgarn and Tanami areas in May/June 2007 and August 2007.
In a recent pilot study, we have demonstrated the feasibility of K/Ar dating minerals such as Beudantite and Plumbojarosite from the oxide zone of ore-bodies in the Cobar region. Our preliminary results indicate Miocene ages, consistent with paleomagnetic results from the same area. We plan to complete a small number of K/Ar analyses, sufficient to publish the results as quickly as possible.
A second edition of the “Regolith Dating methods Handbook” will be completed by October 2007.
In the final 12 months of the CRC, to June 2008, we will make it a high priority to publish geochronology papers in high quality international journals. For example, a manuscript being prepared, with the working title “Weathering through the ages in the Tanami Desert ”, will likely be submitted to Science later this year.
In summary, the project will continue to provide new insights into the chronology and rates of Australian regolith and landscape evolution in selected focus regions.
Deliverables (outputs) and expected impacts of research (outcomes):
Outputs
- LEME report “Regolith Dating Methods” 2nd edition
- Manuscript "Weathering through the ages in the Tanami Desert" to be submitted to Science
- Oral presentation "Geochronology of long-term landscape evolution in northwestern WA" at 13th ANZ Geomorpholoty group Conference in Tasmania, Feb 08
- Manuscript "Paleomagnetic evidence for two periods of intense oxidative weathering at McKinnons Mine, Cobar, NSW" to be submitted to the Australian Journal of Earth Sciences (co-authors Martin Smith and Ken mcQueen)
Outcomes
• Chronologically constrained regolith landform evolution models
• Chronologically constrained geochemical dispersion models
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