The angrites are a class of achondrites that encompass a wide range of igneous textures from quenched, volcanic, and subvolcanic stones to slowly cooled, plutonic rocks. The compositions of the various geochemical reservoirs generating this variety of rocks have not been investigated fully because historically the numbers and masses of angrites available for study have been quite small. However, the rapid increase in meteorites from Northwest Africa (NWA) has enabled a renewed opportunity for such an investigation. In particular, three samples, NWA 2999, 4590, and 4801, have provided a new window into our understanding of the origin and petrogenesis of the coarse‐grained (plutonic) angrites. We report here the trace element abundances in individual mineral grains of pyroxene, plagioclase, olivine/kirschsteinite, and phosphate and in the whole‐rock samples. We utilize these data to constrain the petrogenetic history of each of these samples on the angrite parent body (e.g., parental melt compositions and oxygen fugacity conditions) and assess genetic relationships to previously investigated angrites. The trace element abundances in each of the three coarse‐grained angrites studied here indicate a unique history for each. The observed trace element abundances and patterns in NWA 2999 show similarities with previously studied fine‐grained, volcanic angrites and potentially indicate a common geochemical source reservoir, even though NWA 2999 is temporally distinct from the volcanic angrites. In contrast, NWA 4590 has trace element characteristics analogous to other coarse‐grained angrites (e.g., Lewis Cliff [LEW] 86010), suggesting that these samples originated from geochemically similar source reservoirs. The third angrite, NWA 4801, exhibits geochemical characteristics most similar to the plutonic, coarse‐grained angrites, but also appears to have some affinities in its trace element characteristics to the volcanic, fine‐grained angrites. This suggests that NWA 4801 may represent a petrogenetic link between two distinct geochemical reservoirs on the angrite parent body. In aggregate, the trace element distributions in these three plutonic angrites suggest that while they may have originated up to several million years after the fine‐grained angrites, they sampled a range of source reservoirs on the angrite parent body. Some of these source reservoirs were likely similar to those of the fine‐grained angrites, but others had distinct geochemical characteristics.

中文翻译：

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西北非洲粗粒角质岩的微量元素地球化学：对岩石成岩作用的启示

角质岩是一类长石，涵盖了从火成岩，火山岩和次火山岩到缓慢冷却的深成岩的各种火成岩质地。由于历史上可供研究的角铁的数量和质量一直很小，因此尚未对形成这种岩石的各种地球化学储层的成分进行充分的研究。但是，来自西北非洲（NWA）的陨石的迅速增加为这种调查提供了新的机会。特别是，三个样品NWA 2999、4590和4801为我们对粗粒（成岩型）角砾岩的成因和岩石成因的理解提供了新的窗口。我们在这里报告了辉石，斜长石，橄榄石/钾长石，和磷酸盐以及整个岩石样品中。我们利用这些数据来约束这些样品在角铁母体上的成岩史（例如，父母熔体成分和氧逸度条件），并评估与先前研究的角铁的遗传关系。此处研究的三个粗粒天使中的痕量元素丰度指示了每个元素的独特历史。NWA 2999中观察到的痕量元素丰度和样式显示与先前研究的细粒火山岩相似，即使NWA 2999在时间上与火山岩不同，也可能表明它是一个通用的地球化学源储层。相比之下，NWA 4590具有类似于其他粗粒角铁矿（例如Lewis Cliff [LEW] 86010）的痕量元素特征，这表明这些样品起源于地球化学相似的储层。第三个角砾岩NWA 4801的地球化学特征与深成岩的粗粒角砾岩最为相似，但其痕量元素特征似乎与火山细粒的角砾岩具有某些相似性。这表明，NWA 4801可能代表了Angrite母体上两个不同的地球化学储层之间的岩石成因联系。总的来说，这三种深成岩角质中的微量元素分布表明，尽管它们可能起源于细粒角质岩长达几百万年，但他们还是在角质母体上取样了一系列储层。这些储层中的某些可能与细粒角砾岩的储层相似，但其他储层具有独特的地球化学特征。