RARE-EARTH ABUNDANCES IN CHONDRITIC METEORITES
RARE-EARTH ABUNDANCES IN CHONDRITIC METEORITES
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DOI：
10.1016/0016-7037(78)90114-x
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发表时间：
1978-01-01
影响因子：
5
通讯作者：
ONIONS, RK
中科院分区：
文献类型：
--
作者：
EVENSEN, NM;HAMILTON, PJ;ONIONS, RK
用同位素稀释法分析了15个碳酸盐岩（包括8个碳质碳酸盐岩）的稀土元素丰度。这些分析补充和扩展了早期同位素稀释稀土元素的测定，在其他实验室进行，使主要球粒陨石类的覆盖范围现在是完整的。这一机构的精确和可比的REE数据，从个人的岩石的检查显示，只有一小部分的分析有平坦的，未分馏的REE模式内的实验误差。一个统计程序是用来获得修订的稀土元素丰度的未分馏模式的选择。其余的一些分析显示Eu异常和分馏模式与行星分异产物中遇到的岩浆分馏一致。然而，许多模式表现出的功能不容易解释已知的岩浆过程，特别是积极的Ce异常经常遇到。利用最小二乘曲线拟合方法可以定量地确定异常。各种各样的异常模式和模型参数的不确定性排除了对异常起源的详细建模，但很可能至少有一些是由太阳星云中的部分冷凝引起的，正如阿连德夹杂物所证明的那样。在所有主要的球粒陨石类中都发现了元素丰度异常。如果这些异常被忽略，球粒陨石类内的变化的范围和性质是一致的母体模型，其中的固-液或固-固平衡引起的变化，从未分馏的散装组合物。在H，L和LL母体的绝对丰度几乎是E母体的两倍。异常的持久性在相对直接冷凝过程中删除的球粒陨石材料意味着异常成分是抵抗平衡或在球粒陨石形成的后期阶段引入。大规模的隔离气体和凝析油也暗示，并提出了大规模的行星体之间的稀土元素丰度变化的可能性。
Fifteen chondrites, including eight carbonaceous chondrites, have been analyzed for rare earth element (REE) abundances by isotope dilution. These analyses complement and extend earlier isotope dilution REE determinations in chondrites, performed in other laboratories, so that coverage of major chondrite classes is now complete. An examination of this body of precise and comparable REE data from individual chondrites reveals that only a small proportion of the analyses have flat, unfractionated REE patterns within experimental error. A statistical procedure is used to derive revised chondritic abundances of REE by selection of unfractionated patterns. A number of the remaining analyses show Eu anomalies and fractionated patterns consistent with magmatic fractionation as encountered in the products of planetary differentiation. However, many patterns exhibit features not readily explicable by known magmatic processes; in particular, positive Ce anomalies are often encountered. Abundance anomalies can be quantitatively determined by the use of a least-squares curve fitting procedure. The wide variety of anomalous patterns and the uncertainties in model parameters preclude detailed modeling of the origin of anomalies, but it is probable that at least some arise from fractional condensation in the solar nebula, as has been demonstrated for Allende inclusions. Elemental abundance anomalies are found in all major chondrite classes. If these anomalies are ignored, the range and nature of variation within chondrite classes are consistent with a parent body model, in which solid-liquid or solid-solid equilibria induce variations from an unfractionated bulk composition. Absolute abundances in the H, L and LL parent bodies are almost twice those of the E parent body.The persistence of anomalies in chondritic materials relatively removed from direct condensational processes implies that anomalous components are resistant to equilibration or were introduced at a late stage of chondrite formation. Large scale segregation of gas and condensate is also implied, and raises the possibility of bulk variations in REE abundances between planetary bodies.