Magnesium isotope fractionation in silicate melts by chemical and thermal diffusion
Magnesium isotope fractionation in silicate melts by chemical and thermal diffusion
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DOI：
10.1016/j.gca.2007.10.016
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发表时间：
2008
影响因子：
5
通讯作者：
F. Richter;E. Watson;R. Mendybaev;F. Teng;P. Janney
中科院分区：
文献类型：
--
作者：
F. Richter;E. Watson;R. Mendybaev;F. Teng;P. Janney
采用两种类型的实验室实验来量化与硅酸盐液体中的化学和热(SORET)扩散有关的镁同位素分馏。将熔融的天然玄武岩(SUNY MORB)和熔融的天然流纹岩(莱克县黑暗岩)并列在一起的化学扩散偶在活塞筒装置中运行，用来测定镁从熔融的玄武岩扩散到熔融的流纹岩时的同位素分馏。热扩散实验也是在活塞筒装置中进行的，但将完全由SUNY MORB熔体制成的样品从组装炉的热点移开，使样品从一端到另一端的温差约为100-200°C。化学扩散实验表明，26 mg/24 mg的分馏高达7‰，这导致了β=0.05时与[公式：见文本]相对应的镁同位素的自扩散系数的质量依赖性的估计。热扩散实验表明，在100℃左右的温差作用下，玄武岩中的MgO、CaO和FeO组分在较冷的一端略有富集约1wt%，而在较热的一端则有数wt%的富集度。温度梯度也使镁同位素发生了分馏。约150°C的温差在较冷的一端相对于较热的一端产生了26 mg/24 mg的8‰富集度。玄武岩中镁同位素随温度变化的分馏系数为3.6×10−2‰/°C/amu。
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 of26Mg/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 [Formula: see text] 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 SiO2was 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 of26Mg/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.