Abstract
Recently experiments on He extraction from an amphibole by the incremental heating unexpectedly revealed that the He release pattern depends on the heating rate. During slow heating (~4 K·min−1) of the amphibole grains, one smooth peak of the He flux from the mineral was observed; in contrast, during fast heating (~40 K·min−1) an additional sharp peak appeared at a temperature about 750 °C. In order to explain these observations, we developed a model of He diffusion from the amphibole, which allowed the calculated He fluxes from the mineral to be reconciled with those observed. From the modelling we derived: (i) the helium diffusion domain size distribution, and evolution of the distribution in the course of incremental heating; (ii) occurrence of the tensile stresses, operating under enhanced temperatures above 700 °C. The stresses are different in sites with the different local thermal expansion of the crystalline lattice and they increase the He diffusion flux. The model can be applied to other minerals (materials).
Highlights
The objectives of this study are to present new data on He release from the amphibole grains and powder by fast and slow incremental heating, and to explain the observed release patterns by an adequate diffusion model that takes into account the diffusion domain size distribution and the processes governing He diffusion in the course of heating of the mineral
The He release patterns, measured in the course of the fast and slow incremental heating of the powder and grains of amphibole 23/90, and the heating rates are presented in Figure 1 and Figure 3 and in the Supplementary File; the 4He amounts, released in the extraction experiments, are shown in the captions to these Figures
He is released as a smooth peak within a wider temperature interval compared with that expected from He diffusion from the single size diffusion domain
Summary
Received: 27 October 2020 Accepted: 22 December 2020 Published: 28 December 2020. Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Studies of noble gas mobility in minerals may be contingently separated into two major branches. The first one aims to distinguish the different noble gas components in a mineral, to understand the origin and behavior of each, and to use the results in such fields as radiometric dating, e.g., [1,2,3,4], isotope geochemistry and hydrology [5,6,7,8].
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