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Abstract. Diffusion properties of cosmogenic 3He in quartz at Earth surface temperatures offer the potential to directly reconstruct the evolution of pastin situ temperatures from formerly glaciated areas, which is important information for improving our understanding of glacier–climateinteractions. In this study, we apply cosmogenic 3He paleothermometry to rock surfaces gradually exposed from the Last Glacial Maximum(LGM) to the Holocene period along two deglaciation profiles in the European Alps (Mont Blanc and Aar massifs). Laboratory experiments conducted onone representative sample per site indicate significant differences in 3He diffusion kinetics between the two sites, with quasi-linearArrhenius behavior observed in quartz from the Mont Blanc site and complex Arrhenius behavior observed in quartz from the Aar site, which weinterpret to indicate the presence of multiple diffusion domains (MDD). Assuming the same diffusion kinetics apply to all quartz samples along eachprofile, forward model simulations indicate that the cosmogenic 3He abundance in all the investigated samples should be at equilibrium withpresent-day temperature conditions. However, measured cosmogenic 3He concentrations in samples exposed since before the Holocene indicate anapparent 3He thermal signal significantly colder than today. This observed 3He thermal signal cannot be explained with a realisticpost-LGM mean annual temperature evolution in the European Alps at the study sites. One hypothesis is that the diffusion kinetics and MDD modelapplied may not provide sufficiently accurate, quantitative paleo-temperature estimates in these samples; thus, while a pre-Holocene 3Hethermal signal is indeed preserved in the quartz, the helium diffusivity would be lower at Alpine surface temperatures than our diffusion modelspredict. Alternatively, if the modeled helium diffusion kinetics is accurate, the observed 3He abundances may reflect a complexgeomorphic and/or paleoclimatic evolution, with much more recent ground temperature changes associated with the degradation of alpine permafrost.
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This content will become publicly available on July 1, 2026
Helium Diffusion Kinetics in Enstatite, Kamacite, and Albite, With Implications for the Cosmic Ray Exposure Ages of Enstatite (E) Chondrites
Cosmic ray exposure (CRE) ages are used to constrain the orbital and impact history of meteorites and identify their parent body or source region. CRE ages of enstatite (E) chondrites obtained from measurements of 3He are often much younger than 21Ne CRE ages measured in the same meteorite, which is often attributed to diffusive loss of 3He via solar heating during orbit. With knowledge of the diffusion kinetics of 3He in the major minerals making up E chondrites, we can leverage this discrepancy in CRE ages to infer a meteorite’s recent thermal history. To this end, we performed stepwise degassing experiments on fragments of albite, enstatite and kamacite, the dominant minerals in E chondrites, that were irradiated with protons to produce 3He. We find albite displays simple, Arrhenius-dependent 3He diffusion behavior, whereas enstatite and kamacite exhibit somewhat more complex diffusion behavior. We find that cosmogenic 3He will be readily lost from albite in the space environment, enstatite can exhibit significant 3He loss if exposed to high temperatures characteristic of low perihelion on million year time scales, and kamacite is highly retentive of 3He and unlikely to experience direct diffusive loss. These diffusion kinetics parameters can also be used to understand the exposure and thermal histories of other meteorite classes, terrestrial cosmogenic 3He applications, and mantle noble gas systematics.
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- Award ID(s):
- 2016748
- PAR ID:
- 10650752
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- ACS Earth and Space Chemistry
- Volume:
- 9
- Issue:
- 7
- ISSN:
- 2472-3452
- Page Range / eLocation ID:
- 1881 to 1892
- Subject(s) / Keyword(s):
- helium diffusion enstatite kamacite albite meteorite cosmogenic
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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