The inverse problem of argon diffusion from minerals: Determination of kinetic parameters from stepwise-heating experiments

Stephen B. Brandt; S.V. Rasskazov; I.S. Brandt; A.V. Ivanov; Michael J. Kunk

doi:10.1080/10256019708234052

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The inverse problem of argon diffusion from minerals: Determination of kinetic parameters from stepwise-heating experiments

Stephen B. Brandt·S.V. Rasskazov·I.S. Brandt·A.V. Ivanov·Michael J. Kunk

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Abstract

Results of two routine 40 Ar/ 39 Ar stepwise heating experiments on a biotite and a basanite are interpreted in terms of Fick's and Arrhenius' laws. Both patterns represent a saddle-shaped 39 Ar release. Argon isotope spectra are suggested to be controlled by the activation energy of diffusion E and the frequency factor D o . The activation energy of 39 Ar is lower than the one of 40 Ar. This results in a preferable release of 40 Ar relatively to 39 Ar at high-temperature steps and an increasing high-temperature wing in the saddle-shaped age spectrum. At low temperatures, considerable losses and irregularities in release of mainly 39 Ar are observed, which cause the decreasing low-temperature wing in the “saddle”. The suggestion of argon losses (mainly of 39 Ar) from a loose, “unstable” zone of the mineral structures becomes justified. The n -irradiation of the samples and the shift of E of 39 Ar towards lower values seems to explain the saddle-shaped age-spectra often encountered in 40 Ar/ 39 Ar-geochronometry.

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Stephen B. Brandt, S.V. Rasskazov, I.S. Brandt, A.V. Ivanov, Michael J. Kunk. 1997. The inverse problem of argon diffusion from minerals: Determination of kinetic parameters from stepwise-heating experiments. https://doi.org/10.1080/10256019708234052

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