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Argon retention properties of silicate glasses and implications for 40Ar/39Ar age and noble gas diffusion studies

Sized aggregates of glasses (47-84 wt% SiO2) were fused from igneous-derived cohesive fault rock and igneous rock, and step-heated from approximately 400 to >1,200 degrees C to obtain their 39Ar diffusion properties (average E=33,400 cal molm1; Do=4.63210m3 cm2 sm1). At T< approximately 1,000...

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Bibliographic Details
Published in:Contributions to mineralogy and petrology 2003-04, Vol.145 (1), p.1-14
Main Authors: Hazelton, Garrett B., Axen, Gary, Lovera, Oscar
Format: Article
Language:English
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Summary:Sized aggregates of glasses (47-84 wt% SiO2) were fused from igneous-derived cohesive fault rock and igneous rock, and step-heated from approximately 400 to >1,200 degrees C to obtain their 39Ar diffusion properties (average E=33,400 cal molm1; Do=4.63210m3 cm2 sm1). At T< approximately 1,000 degrees C, glasses containing < approximately 69 wt% SiO2 and abundant network-forming cations (Ca, Fe, Mg) reveal moderate to strong non-linear increases in D and E, reflecting structural modifications as the solid transitions to melt. Extrapolation of these Arrhenius properties down to typical geologic T-t conditions could result in a 1.5 log10 unit underestimation in the diffusion rate of Ar in similar materials. Numerical simulations based upon the diffusion results caution that some common geologic glasses will likely yield 40Ar/39Ar cooling ages rather than formation ages. However, if cooling rates are sufficiently high, ambient temperatures are sufficiently low (e.g., approximately 1 mm) are analyzed, glasses with compositions similar to ours may preserve their formation ages. [PUBLICATION ABSTRACT]
ISSN:0010-7999
1432-0967
DOI:10.1007/s00410-003-0440-7