Partitioning of oxygen between the Earth's mantle and core
Partitioning of oxygen between the Earth's mantle and core
复制标题
DOI：
10.1029/2009jb006302
复制
发表时间：
2010-02-10
影响因子：
3.9
通讯作者：
Sakai, Takeshi
中科院分区：
文献类型：
--
作者：
Frost, Daniel J.;Asahara, Yuki;Sakai, Takeshi
在30-70 GPa和2800-3500 K条件下，用激光加热金刚石对顶砧装置研究了氧在铁液和（Mg，Fe）O镁橄榄石之间的分配。使用聚焦离子束从回收样品中的反应区域制备薄箔。用透射电子显微镜结合X射线能谱和电子能量损失谱测量了共存淬火铁和镁橄榄石的成分。为了理解和模拟结果，进行了额外的实验以确定液态Fe金属中氧或FeO的活性。多砧实验，以测量共存的不混溶的金属和离子液体中的Fe-FeO系统的氧含量进行了高达25 GPa。结果被用来提取多余的混合性质的Fe-FeO液体在高压和高温。这些属性被用来推导出一个模型，该模型描述了在Fe-Mg-O系统，是独立的实际实验分区数据的氧分区。该模型表明，在压力大于25 GPa时，液态铁的氧含量成为镁橄榄石的FeO含量的强非线性函数。这种预测是在很好的协议与实验分区数据，这是忠实地再现在大多数情况下。新的结果证实，地球的核心是不饱和的氧相对于FeO含量的大部分地幔，这将导致在FeO被耗尽从地幔的最底部或导致发展的FeO富集外层的核心。这些可能性并不相互排斥。
Experiments to investigate the partitioning of oxygen between liquid iron and (Mg,Fe)O magnesiowustite were conducted at 30-70 GPa and 2800-3500 K using a laser-heated diamond anvil cell. A thin foil was prepared from the reacted regions in the recovered samples using a focused ion beam. The compositions of coexisting quenched iron and magnesiowustite were measured using a transmission electron microscope equipped with energy dispersive X-ray spectroscopy and electron energy-loss spectroscopy. In order to understand and model the results, additional experiments were performed to determine the activity of oxygen, or rather FeO, in liquid Fe metal. Multianvil experiments to measure the oxygen contents of coexisting immiscible metallic and ionic liquids in the Fe-FeO system were performed up to 25 GPa. The results were used to extract excess mixing properties for Fe-FeO liquids at high pressure and temperature. These properties were used to derive a model that describes oxygen partitioning in the Fe-Mg-O system that is independent of the actual experimental partitioning data. The model indicates that the oxygen content of liquid Fe becomes a strong nonlinear function of the FeO content of magnesiowustite at pressures greater than 25 GPa. This prediction is in excellent agreement with the experimental partitioning data, which is faithfully reproduced in most instances. The new results confirm that the Earth's core is undersaturated in oxygen with respect to the FeO content of the bulk mantle, which will result either in FeO being depleted from the very base of the mantle or lead to the development of an FeO-enriched outer layer of the core. These possibilities are not mutually exclusive.