20-EPN2-017: Resolving critical uncertainties in the impact of geomagnetism on in situ cosmogenic nuclide production via long-term calibration
Visit by Gordon Bromley, University of Galway (Ireland), to TA2.9 Ion Probe Facility (IPF), CRPG (France).
Dates of visit: 17 – 21 October 2022
Report Summary: Cosmogenic nuclide (CN) surface-exposure dating (SED) has revolutionised geomorphology in recent years, enabling the direct determination of both the rate and age of Earth surface-processes. However, SED relies on strict quantification of CN production rates (PRs) for both the time-period and location in question; for many sites and times periods such data is rare. As a result, calculated exposure ages may vary significantly depending upon the assumptions and model schemes employed in calculations. The impact of geomagnetic field variability on nuclide production is particularly uncertain.
The goal of this project is to test explicitly the methods used to calculate exposure ages, and to assess their viability over space and time. To do this, we measured cosmogenic helium-3 within a series of Peruvian lavas of varying age at the Stable Rare Gas and Radiogenic Isotope Facility, CRPG (France). Paired with later Ar/Ar age determination, we are using these new cosmogenic helium data to produce a series of discrete CN production rates from a single geographic region, and so will assess the variability of nuclide production through time. Our preliminary results indicate the research plan is viable: cosmogenic helium data from single lava flows are internally consistent. Lavas analysed range in age from ~1.6 ka to ~175 ka, and so provide a dataset that spans a period sufficient to assess changes in PR and the potential impact of magnetic field variability on CN PRs. We anticipate sharing final project results within a peer-reviewed, open-access publication within the calendar year.
Read the full scientific report, with kind permission from Gordon Bromley.
