Earth and Planetary Science
EPS Near-Surface Geochemistry and Geobiology

Berkeley Scientists Study Neon Diffusion Kinetics to Gain Insights into Cosmogenic Neon Paleothermometry in Feldspars

Wednesday, February 22, 2017

Marissa Tremblay, David Shuster and Greg Balco are co-authors of “Neon diffusion kinetics and implications for cosmogenic neon paleothermometry in feldspars.” The research article came out in the journal Geochimica et Cosmochimica Acta.

The applicability of cosmogenic neon to either application depends on the temperature-dependent diffusivity of neon isotopes. In this work, the researchers investigate the kinetics of neon diffusion in feldspars of different compositions and geologic origins through stepwise degassing experiments on single, proton-irradiated crystals. To understand the potential causes of complex diffusion behavior that is sometimes manifest as nonlinearity in Arrhenius plots, they compare our results to argon stepwise degassing experiments previously conducted on the same feldspars. Many of the feldspars they studied exhibit linear Arrhenius behavior for neon whereas argon degassing from the same feldspars did not. This suggests that nonlinear behavior in argon experiments is an artifact of structural changes during laboratory heating. However, other feldspars that we examined exhibit nonlinear Arrhenius behavior for neon diffusion at temperatures far below any known structural changes, which suggests that some preexisting material property is responsible for the complex behavior. In general, neon diffusion kinetics vary widely across the different feldspars studied, with estimated activation energies (Ea) ranging from 83.3 to 110.7 kJ/mol and apparent pre-exponential factors (D0) spanning three orders of magnitude from 2.4 x 10-3 to 8.9 x 10-1 cm2s-1. As a consequence of this variability, the ability to reconstruct temperatures or exposure durations from cosmogenic neon abundances will depend on both the specific feldspar and the surface temperature conditions at the geologic site of interest.

Marissa Tremblay is a doctoral candidate in the Berkeley Earth & Planetary Science Department. David Shuster is professor in EPS; he is primarly focused on understanding processes that occur at or near the surfaces of Earth, Mars, and Earth’s moon. Greg Balco is visiting associate researcher in the department and in the Berkeley Geochronology Center.

For the full-length article please click here.