10.6084/m9.figshare.3453338.v1
Marnie A. Forster
Marnie A.
Forster
Gordon S. Lister
Gordon S.
Lister
<sup>40</sup>Ar/<sup>39</sup>Ar geochronology and the diffusion of <sup>39</sup>Ar in phengite–muscovite intergrowths during step-heating experiments <em>in vacuo</em>
Geological Society of London
2016
extensional ductile shear zones
experiment
diffusion
geochronology
mica mineral growth
39 Ar
Geology
2016-06-21 11:19:14
Dataset
https://geolsoc.figshare.com/articles/dataset/_sup_40_sup_Ar_sup_39_sup_Ar_geochronology_and_the_diffusion_of_sup_39_sup_Ar_in_phengite_muscovite_intergrowths_during_step-heating_experiments_em_in_vacuo_em_/3453338
<p>Step-heating experiments <em>in vacuo</em> are routine when conducting <sup>40</sup>Ar/<sup>39</sup>Ar geochronology, including for white mica. White mica can break down, due to dehydroxylation and delamination, so experiments
involving mica are often conducted in relative haste, and not with the care and precision necessary when intending to apply
multi-diffusion-domain theory to model the results. Here we show, however, that carefully managed step-heating experiments
appear to allow release of argon through solid-state diffusion processes alone. We analysed phengite-muscovite intergrowths
in high-pressure metamorphic rocks exhumed in and beneath extensional ductile shear zones during continental extension. Such
materials often yield Arrhenius plots in which there is a distinct steepening of slope mid-way through the step-heating sequence.
This steepening appears to correspond with steps in which release of argon from phengite components dominate. We analysed
the data using a computer program (<em>eArgon</em>) and numerically simulated mixing of gas released from multiple diffusion domains. The results suggest that diffusion of
<sup>39</sup>Ar in phengitic white mica involves radically different diffusion parameters in comparison with muscovite. If these results
extrapolate to nature then <sup>40</sup>Ar/<sup>39</sup>Ar geochronology may allow direct dating of white mica mineral growth during metamorphism.
</p>