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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 >Enstatite chondrites EL3 as building blocks for the Earth: The debate over the Sm-146-Nd-142 systematics
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Enstatite chondrites EL3 as building blocks for the Earth: The debate over the Sm-146-Nd-142 systematics

机译：Enstatite Chondrites El3作为地球的构建块：SM-146-ND-142系统的辩论

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摘要

The (SmNd)-Sm-146-Nd-142 extinct decay scheme (Sm-146 half-life of 103 My) is a powerful tool to trace early Earth silicate differentiation. Differences in Nd-142 abundance measured between different chondrite meteorite groups and the modern Earth challenges the interpretation of the Nd-142 isotopic variations found in terrestrial samples because the origin of the Earth and the nature of its building blocks is still an ongoing debate. As bulk meteorites, the enstatite chondrites (EC) have isotope signatures that are the closest to the Earth value with an average small deficit of similar to 10 ppm in Nd-142 relative to modern terrestrial samples. Here we review all the Nd isotope data measured on EC so far, and present the first measurements on an observed meteorite fall Almahata Sitta containing pristine fragments of an unmetamorphosed enstatite chondrite belonging to the EL3 subgroup. Once Nd-142/Nd-144 ratios are normalized to a common chondritic evolution, samples from the EC group (both EL and EH) have a deficit in Nd-142 but the dispersion is important (mu Nd-142 = -10 +/- 12 (2SD) ppm). This scatter reflects their unique mineralogy associated to their formation in reduced conditions (low fO(2) or high C/O). Rare-earth elements are mainly carried by the sulfide phase oldhamite (CaS) that is more easily altered than silicates by weathering since most of the EC meteorites are desert finds. The EL6 have fractionated rare-earth element patterns with depletion in the most incompatible elements. Deviations in Nd mass independent stable isotope ratios in enstatite chondrites relative to terrestrial standard are not resolved with the level of analytical precision achieved by modern mass spectrometry techniques. Here we show that enstatite chondrites from the EL3 and EL6 subgroups may come from different parent bodies. Samples from the EL3 subgroup have Nd (mu Nd-142 = -0.8 +/- 7.0, 2SD) and Ru isotope ratios undistinguishable from that of the Bulk Silicate Earth. EL3 s
机译：（SMND）-SM-146-ND-142灭绝衰变方案（SM-146半衰期为103我的半衰期）是追踪早期地球硅酸盐分化的强大工具。在不同的嗜乳头陨石群和现代地球之间测量的ND-142丰度的差异挑战陆地样品中发现的ND-142同位素变异的解释，因为地球的起源和其构建块的性质仍然是一个正在进行的辩论。作为散象，脑牙石软骨素（EC）具有同位素签名，该同位素签名是最接近的地球价值，其平均小缺陷在与现代陆地样品中的ND-142中的10 ppm相似。在这里，我们审查了迄今为止在EC上测量的所有ND同位素数据，并在观察到的陨石秋季Almahata sitta上呈现了含有属于EL3亚组的未掩盖的未常见的脑霉菌的原始片段的第一测量。一旦ND-142 / ND-144比率归一化到常见的软体中的进化，来自EC组（EL和EH）的样品在ND-142中具有缺陷，但分散是重要的（MU ND-142 = -10 + / - 12（2SD）PPM）。该散射反映了它们在减少条件下与其形成相关的独特矿物质（低FO（2）或高C / O）。稀土元素主要由硫化物相结晶醛（CAS）携带，从静音比硅酸盐更容易改变，因为大多数EC陨石都是沙漠发现。 EL6在最不相容的元件中具有耗尽的分级稀土元素图案。 ND大众独立稳定同位素比在相对于陆地标准的脑卒多体中的偏差没有通过现代质谱技术实现的分析精度水平来解决。在这里，我们表明来自EL3和EL6子组的Enstatite Chondrites可能来自不同的父体。来自EL3亚组的样品具有Nd（mu Nd-142 = -0.8 +/- 7.0，2sd），并且Ru同位素比与散装硅酸盐地球的无区别不可替补。 el3 s.

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