Diffusive fractionation of K isotopes in molten basalts
نویسندگان
چکیده
The 41K/39K isotope ratio profiles in diffusion couple experiments have been measured by Secondary Ion Mass Spectrometry (SIMS). One goal of this research is to push the use SIMS measuring non-traditional stable ratios. second, more important goal, quantify for first time diffusive fractionation K isotopes and its dependence on temperature different counter-diffusion elements. data show that precision a single day-night session measurements can reach 0.2‰ (1? hereafter) with effort, long-term accuracy without using any standard about 2.5‰. At an initial concentration contrast (ratio high low concentration) 70 couple, total (maximum minus minimum) 10‰. were initially fit assuming constant effective binary diffusivity (D) K2O, which led minor misfits importantly, large disagreement between diffusivities based chemical profiles. It was found D K2O varies concentration. then increases exponentially concentration, resolved disagreements. That is, combining enables distinguishing subtle concentration-dependent diffusivity. For SiO2-K2O interdiffusion couples, empirical parameter ? slightly from 0.104 ± 0.003 at 1260 °C 0.116 1500 °C. MgO-K2O excluding outlier point °C, 0.090 0.005 1350 0.100 These values are roughly consistent mechanism NaKO exchanging SiO2 or MgO couples. Applying obtained value model nature, during magma mixing expected be enough resolvable SIMS. When collecting samples K-Ar K-Ca dating, it correct effect possible sample. convective-diffusive modeling applied evaluate volatile loss through evaporation, 80% potassium would lead increase ?41K 6.3‰ 8.9‰, than 10 times greater enrichment Moon relative Earth. Hence, depletion associated Earth unlikely controlled.
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ژورنال
عنوان ژورنال: Earth and Planetary Science Letters
سال: 2022
ISSN: ['1385-013X', '0012-821X']
DOI: https://doi.org/10.1016/j.epsl.2022.117405