2018
DOI: 10.1016/j.chemgeo.2018.06.005
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Numerical models of P–T, time and grain-size controls on Ar diffusion in biotite: An aide to interpreting 40Ar/39Ar ages

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Cited by 11 publications
(9 citation statements)
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References 60 publications
(167 reference statements)
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“…Small Bt and Wm grains might have been contaminated by excess 40 Ar, likely related to metamorphic fluids, whereas at least the cores of the larger grains appear not to have been (Warren et al, 2012). This contamination may have occurred at relatively low temperatures (400 -450°C), or during a short lived infiltration event: at such temperatures, the Ar isotopic system in Wm is less sensitive to contamination than in Bt (Kirkland et al, 2008a;Warren et al, 2011;Skipton et al, 2018), leading to the very much older ages in Bt compared to Wm. The effect of such contamination seems to be proportional to the amount of metamorphic re-equilibration experienced by the nappes during Caledonian collision.…”
Section: Effects Of Caledonian Metamorphism On 40 Ar/ 39 Ar Agesmentioning
confidence: 99%
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“…Small Bt and Wm grains might have been contaminated by excess 40 Ar, likely related to metamorphic fluids, whereas at least the cores of the larger grains appear not to have been (Warren et al, 2012). This contamination may have occurred at relatively low temperatures (400 -450°C), or during a short lived infiltration event: at such temperatures, the Ar isotopic system in Wm is less sensitive to contamination than in Bt (Kirkland et al, 2008a;Warren et al, 2011;Skipton et al, 2018), leading to the very much older ages in Bt compared to Wm. The effect of such contamination seems to be proportional to the amount of metamorphic re-equilibration experienced by the nappes during Caledonian collision.…”
Section: Effects Of Caledonian Metamorphism On 40 Ar/ 39 Ar Agesmentioning
confidence: 99%
“…The Eidvågeid Series subsequently resided at high-T, lower crustal conditions for at least 200 Ma prior to the Caledonian orogeny (Gasser et al, 2015). Such long-lasting high-T conditions are theoretically sufficient to completely reset the isotopic system in biotite in an open system where a sink such as a grain boundary fluid is available for the released argon (Skipton et al, 2018). We therefore interpret the 40 Ar/ Ar date of 423.9 ± 6.5 Ma obtained from the mylonitic Eidvågeid sample 240 as relating to the timing of cooling during the late stages of the Celdonian orogeny.…”
Section: Effects Of Caledonian Metamorphism On 40 Ar/ 39 Ar Agesmentioning
confidence: 99%
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“…However, although it is tempting to correlate numerical dates to the ages of known, large-scale tectonic events, we also must consider the potential caveats of the 40 Ar/ 39 Ar systematics, specifically 40 Ar diffusion. Long-term (Myr to Gyr) residence of rocks at ambient midcrustal temperatures, slightly above the~300 • C closure temperature of biotite, may lead to efficient Ar diffusion or partial Ar retention [62]. Numerical modelling of K-feldspar 40 Ar/ 39 Ar data from the Neoarchean rocks of the western Superior Province [63] indicates the craton was at temperatures >325 • C pre-2400 Ma and slowly cooled~100 • C (325-225 • C) over 1 Gyr (2400-1400 Ma; cooling rate of 0.1 • C/Ma).…”
Section: Post-mineralization Hydrothermal Activitymentioning
confidence: 99%
“…Discordance at temperatures above 600 • C is amplified by dramatic changes in the crystal structure of biotite in response to dehydroxylation and oxidation [7]. Therefore, explanations of the disturbed 40 Ar/ 39 Ar age spectra and derivation of meaningful 40 Ar/ 39 Ar ages from biotite is a long-standing challenge [2,4,[7][8][9][10][11][12].…”
Section: Introductionmentioning
confidence: 99%