Silicon in the metal phase of enstatite chondrites and some geochemical implications
Silicon in the metal phase of enstatite chondrites and some geochemical implications
复制标题
顽辉石球粒陨石金属相中的硅及其一些地球化学意义
DOI：
10.1016/0016-7037(61)90056-4
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发表时间：
1961
影响因子：
5
通讯作者：
A. .. Ringwood
中科院分区：
文献类型：
--
作者：
A. .. Ringwood
最近的一些假说提出，硅是地球核心的主要组成部分。由于地球的化学演化在某些方面可能与陨石中发生的类似，因此在陨石的金属相中寻找硅。使用X射线和化学方法，确定了在所检查的所有八种顽火辉石的金属相中，2至6原子%的硅以固溶体形式存在。在普通陨石的金属相中没有发现硅。本文评述了有关地核中可能存在硅的证据，并较详细地讨论了与这一假说有关的新陨石数据的意义。对伴随地核分凝的条件的研究，包括在地球和母陨石中的分凝，得出的结论是，地核不太可能与周围的地幔处于化学平衡状态。这种不平衡的主要影响之一是硅从地核扩散到地幔的邻近区域，导致氧化铁的还原和金属铁的沉淀。这种效应可能是造成地幔底部200 km处地震速度梯度异常的原因。这一区域可能是机械不稳定的，因为沉淀的铁倾向于聚集并沉入地核。由于这一区域的离子和电子输运性质的不均匀性，在地核-地幔边界上达到化学平衡伴随着电流的产生。这可能与地球磁场的起源有关，也可能影响核幔之间的电磁耦合。
Some recent hypotheses have proposed that silicon occurs as a major component of the earth's core. Since the chemical evolution of the earth may have been analogous in some respects to that which occurred in meteorites, a search for silicon was made in the metal phases of chondrites. Using X-ray and chemical methods, it was established that between 2 and 6 atomic per cent of silicon occurred in solid solution in the metal phases of all eight enstatite chondrites which were examined. No silicon was found in the metal phase of ordinary chondrites.Evidence relating to the possible occurrence of silicon in the earth's core is reviewed, and the significance of the new meteoritic data in relation to this hypothesis is discussed in some detail.A study of the conditions which accompany the segregation of a core, both in the earth and in the parent meteoritic body, lead to the conclusion that the core is unlikely to be in chemical equilibrium with the surrounding mantle. One of the principal effects of this disequilibrium is the diffusion of silicon from the core into the adjacent region of the mantle, resulting in the reduction of oxidized iron and precipitation of metallic iron. This effect may be responsible for the anomalous seismic velocity gradients which are observed in the bottom 200 km of the mantle. This region is likely to be mechanically unstable, owing to the tendency of precipitated iron to collect and sink into the core.Owing to inhomogenieties in ionic and electronic transport properties in this region, attainment of chemical equilibrium across the core-mantle boundary is accompanied by generation of electric currents. These may be relevant to the origin of the earth's magnetic field, and may also affect the electromagnetic coupling between core and mantle.