1. Magnesium isotope fractionation in silicate melts by chemical and thermal diffusion
- Author
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Richter, Frank M., Watson, E. Bruce, Mendybaev, Ruslan A., Teng, Fang-Zhen, and Janney, Philip E.
- Subjects
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DIFFUSION , *MAGNESIUM , *IGNEOUS rocks , *ISOTOPES - Abstract
Abstract: Two types of laboratory experiments were used to quantify magnesium isotopic fractionations associated with chemical and thermal (Soret) diffusion in silicate liquids. Chemical diffusion couples juxtaposing a molten natural basalt (SUNY MORB) and a molten natural rhyolite (Lake County Obsidian) were run in a piston cylinder apparatus and used to determine the isotopic fractionation of magnesium as it diffused from molten basalt to molten rhyolite. The thermal diffusion experiments were also run in a piston cylinder apparatus but with a sample made entirely of molten SUNY MORB displaced from the hotspot of the assembly furnace so that the sample would have a temperature difference of about 100–200°C from one end to the other. The chemical diffusion experiments showed fractionations of 26Mg/24Mg by as much as 7‰, which resulted in an estimate for the mass dependence of the self-diffusion coefficients of the magnesium isotopes corresponding to with β =0.05. The thermal diffusion experiments showed that a temperature difference of about 100°C resulted in the MgO, CaO, and FeO components of the basalt becoming slightly enriched by about 1wt% in the colder end while SiO2 was enriched by several wt% in the hotter end. The temperature gradient also fractionated the magnesium isotopes. A temperature difference of about 150°C produced an 8‰ enrichment of 26Mg/24Mg at the colder end relative to the hotter end. The magnesium isotopic fractionation as a function of temperature in molten basalt corresponds to 3.6×10−2‰/°C/amu. [Copyright &y& Elsevier]
- Published
- 2008
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