陨石和地球中的钍异常和稀土元素模式：星云分馏和块金效应
Thulium anomalies and rare earth element patterns in meteorites and Earth: Nebular fractionation and the nugget effect
摘要：
本文报道了41种辉长岩的稀土元素组成，其中32种来自碳质（CI、CM、CO和CV）、顽火辉石（EH和EL）和普通（H、L和LL）族，9种来自顽火辉石族，2种来自顽火辉石无球粒陨石（Aubrite）族。CI球粒陨石标准化的稀土元素模式和Eu异常在普通和顽火辉石中表现出更分散在更多的变质比在不平衡的顽火辉石。这是由于在变质作用过程中，稀土元素在不同载体相中的母体再分配所致。平衡的普通方解石的稀土模式的分散解释与浓度的稀土在磷酸盐微粒的块金效应。陆源岩石和普通辉石和顽火辉石样品显示相对于钙辉石~-4.5%的负Tm异常。相比之下，CM、CO和CV（除Allanum外）未显示出显著的Tm异常。Allenitic CV球粒陨石显示出大的过量Tm（~+10%）。这些异常与陨石中II组耐火包裹体中发现的异常相似，但幅度要小得多。在陨石和陆地岩石中存在Tm异常表明：（i）太阳系内部的物质是由一个已经耗尽了耐火尘埃并携带Tm正异常的气体储层形成的;或者（ii）CI陨石富含耐火尘埃，并不代表耐火元素的太阳组成。在普通和顽火辉石和陆地岩石中观察到的Tm异常，相对于碳质顽火辉石，表明类似于碳质顽火辉石的物质必须代表地球成分的一小部分。
英文摘要：
This study reports the bulk rare earth element (REEs, La-Lu) compositions of 41 chondrites, including 32 falls and 9 finds from carbonaceous (CI, CM, CO and CV), enstatite (EH and EL) and ordinary (H, L and LL) groups, as well as 2 enstatite achondrites (aubrite). The CI-chondrite-normalized REE patterns and Eu anomalies in ordinary and enstatite chondrites show more scatter in more metamorphosed than in unequilibrated chondrites. This is due to parent-body redistribution of the REEs in various carrier phases during metamorphism. The dispersion in REE patterns of equilibrated ordinary chondrites is explained by the nugget effect associated with concentration of REEs in minor phosphate grains. Terrestrial rocks and samples from ordinary and enstatite chondrites display negative Tm anomalies of ~-4.5 % relative to ca chondrites. In contrast, CM, CO and CV (except Allende) show no significant Tm anomalies. Allende CV chondrite shows large excess Tm (~+10 %). These anomalies are similar to those found in group II refractory inclusions in meteorites but of much smaller magnitude. The presence of Tm anomalies in meteorites and terrestrial rocks suggests that either (i) the material in the inner part of the solar system was formed from a gas reservoir that had been depleted in refractory dust and carried positive Tm anomalies or (ii) CI chondrites are enriched in refractory dust and are not representative of solar composition for refractory elements. The observed Tm anomalies in ordinary and enstatite chondrites and terrestrial rocks, relative to carbonaceous chondrites, indicate that material akin to carbonaceous chondrites must have represented a small fraction of the constituents of the Earth.
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