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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Early Earth differentiation
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Early Earth differentiation

机译：早期地球分化

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The birth and infancy of Earth was a time of profound differentiation involving massive internal reorganization into core, mantle and proto-crust, all within a few hundred million years of solar system formation (to). Physical and isotopic evidence indicate that the formation of iron-rich cores generally occurred very early in planetesimals, the building blocks of proto-Earth, within about 3 million years of to. The final stages of terrestrial planetary accretion involved violent and tremendously energetic giant impacts among core-segregated Mercury- to Mars-sized objects and planetary embryos. As a consequence of impact heating, the early Earth was at times partially or wholly molten, increasing the likelihood for high-pressure and high-temperature equilibration among core- and mantle-forming materials. The Earth's silicate mantle harmoniously possesses abundance levels of the siderophile elements Ni and Co that can be reconciled by equilibration between iron alloy and silicate at conditions comparable to those expected for a deep magma ocean. Solidification of a deep magma ocean possibly involved crystal-melt segregation at high pressures, but subsequent convective stirring of the mantle could have largely erased nascent layering. However, primitive upper mantle rocks apparently have some nonchondritic major and trace element refractory lithophile element ratios that can be plausibly linked to early mantle differentiation of ultra-high-pressure mantle phases. The geochemical effects of crystal fractionation in a deep magma ocean are partly constrained by high-pressure experimentation. Comparison between compositional models for the primitive convecting mantle and bulk silicate Earth generally allows, and possibly favors, 10-15% total fractionation of a deep mantle assemblage comprised predominantly of Mg-perovskite and with minor but geochemically important amounts of Ca-perovskite and ferropericlase. Long-term isolation of such a crystal pile is generally consistent with isotopic constraints for time-integrated Sm/Nd and Lu/Hf ratios in the modem upper mantle and might account for the characteristics of some mantle isotope reservoirs. Although much remains to be learned about the earliest formative period in the Earth's development, a convergence of theoretical, physical, isotopic and geochemical arguments is beginning to yield a self-consistent portrait of the infant Earth. (C) 2004 Published by Elsevier B.V.
机译：地球的诞生和婴儿期是一个高度分化的时代，涉及大规模内部重组为核心，地幔和原始地壳，所有这些都在太阳系形成的几亿年内完成。物理和同位素证据表明，富含铁的核的形成通常发生在大约300万年前的行星小行星中，这是原始地球的组成部分。地球行星积聚的最后阶段涉及到由核分离出的水星到火星大小的物体以及行星胚胎之间的剧烈剧烈碰撞。冲击加热的结果是，早期地球有时会部分或全部熔化，从而增加了形成岩心和地幔的材料之间发生高压和高温平衡的可能性。地球的硅酸盐地幔和谐地拥有大量的嗜铁元素Ni和Co，可以通过铁合金和硅酸盐之间的平衡来调和，而铁矿石和硅酸盐的条件可与深部岩浆海洋相媲美。深部岩浆海洋的凝固可能涉及高压下的结晶熔体偏析，但随后对流层的对流搅拌可能会大大消除新生层。然而，原始的上地幔岩石显然具有一些非软骨岩的主要元素和微量元素难熔的亲石元素比例，这可能与超高压地幔相的早期地幔分化有关。深部岩浆海洋中晶体分离的地球化学效应受到高压实验的部分限制。原始对流地幔和大块硅酸盐地球的成​​分模型之间的比较通常允许并且可能有利于深地幔组合的总馏分的10-15％，主要由镁钙钛矿组成，并含有少量但在地球化学上很重要的钙钙钛矿和铁硅橡胶酶。这种晶体堆的长期隔离通常与现代上地幔中时间积分的Sm / Nd和Lu / Hf比值的同位素约束相一致，并且可能解释了某些地幔同位素储层的特征。尽管关于地球发展的最早形成期还有很多要学的东西，但理论，物理，同位素和地球化学论证的融合开始产生出对婴儿地球的自相一致的描述。 （C）2004由Elsevier B.V.发布

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