The distribution of Mg and Fe2+ between olivine and spinel at 1300oC
The distribution of Mg and Fe2+ between olivine and spinel at 1300oC
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1300oC 时橄榄石和尖晶石中 Mg 和 Fe2 的分布
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发表时间：
2007
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通讯作者：
PBren L. Roeoen
中科院分区：
文献类型：
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作者：
HeerHen E. JnuresoNl;PBren L. Roeoen
测定了镁和亚铁在橄榄石和铝酸盐尖晶石之间以及橄榄石和铁素体尖晶石之间的平衡分布，以了解镁和亚铁在基性岩和超基性岩中的相互关系。在金属铁存在下，用铝酸盐尖晶石（MgAl2O4-FeAl2Oa）平衡了一系列橄榄石（MgzSiO+-Fe2SiOa）。分布系数KBkr:（xrl ./XFl'.）' （& r-lxilt）在1300摄氏度时接近于1：它在0.94和1.23之间变化，并随着Xftlr的增加而增加。在MgGSiOTFeO-Fe2O3体系中，橄榄石与铁素体尖晶石（MgFezOr） （Mf) - FerO+ (Mt)）作为两相组合或与辉石或液体作为三相组合进行平衡。镁相对于铁素体尖晶石优先分配到橄榄石中，分配系数Ktr-{}:（8}”/& {.,.）6 $“* / X{[”;变化在6.7和9.3之间在13fi)”C。利用分布系数随尖晶石组成的系统变化，计算了铝酸盐和铁素体固溶体的活度—组成关系。假设橄榄石固溶体是理想的，而尖晶石固溶体是规则的，单位的，相对于镁和亚铁，在1300”C。实验结果表明，铝酸盐近乎理想，可以用规则的对称溶液模型很好地描述，其相互作用参数为-3.1+0.6 kJ/mol，平衡常数K“l-”1 = 0.97+0.08 （13fi）”C。铁素体固溶体符合lYrvrr = z-r2kllmol, W1a1 = 7-+4 kJ/mol，平衡常数为不对称模型。在1300℃时，Kol-{t - 7-+l。如果假设17”r = 4.2 kllmol的非理想橄榄石重新计算尖晶石溶液性质，则活性-组成关系和平衡常数都不会发生显着变化。这些新的热力学数据可用于：(1)校正橄榄石-尖晶石地温计，(2)校正橄榄石-正辉石-尖晶石和橄榄石-硅-尖晶石氧地球气压计，以及(3)计算地幔组合中的其他反应。
The equilibrium distribution of magnesium and ferrous iron between olivine and aluminate spinel, and between olivine and ferrite spinel, was determined at 13fi)'C in order to understand the relationship between these phases in mafic and ultramafic rocks. A series of olivines (MgzSiO+-Fe2SiOa) were equilibrated with aluminate spinels (MgAl2O4-FeAl2Oa) in the presence of metallic iron. The distribution coefficient KBkr : (X Rl./XFl'.) ' (&t r-lxilt) is close to one at 1300'C: it varies between 0.94 and 1.23, and increases with Xftlr. Olivines were equilibrated with ferrite spinels (MgFezOr) (Mf) - FerO+ (Mt)) as two-phase assemblages, or with pyroxene or liquid as three-phase assemblages in the system MgGSiOTFeO-Fe2O3. Magnesium is preferentially partitioned into olivine relative to ferrite spinel, and the distribution coefficient Ktr-{' : (8}"/&'.,.) 6$"*/X{["; varies between 6.7 and 9.3 at 13fi)"C. The systematic variation of the distribution coefficient with spinel composition was used to calculate the activity--composition relations of both the aluminate and the ferrite solid solutions. It was assumed that the olivine solid solution is ideal, and that the spinel solid solutions are regular and single-sited, with respect to magnesium and ferrous iron, at 1300"C. The experimental results show that the aluminates are nearly ideal, and can be well described by a regular, symmetric solution model with an interaction parameter 17"1 of -3.1+0.6 kJ/mole, and equilibrium constant K"l-"1 = 0.97+0.08 at 13fi)"C. The ferrite solid solution appears to fit an asymmetric model with lYrvrr = z-r2kllmole and W1a1 = 7-+4 kJ/mole, and equilibrium constant .Kol-{t - 7-+l at 1300'C. If the spinel solution properties are recalculated assuming non-ideal olivines with l7"r = 4.2 kllmole, neither activity-composition relations nor the equilibrium constants are changed significantly. These new thermodynamic data may be applied to: (l) calibration of the olivine-spinel geothermometer, (2) calibration of the olivine-orthopyroxene-spinel and olivine-silica-spinel oxygen geobarometers, and (3) calculation ofother reactions in mantle assemblages.