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首页> 外文期刊>Contributions to Mineralogy and Petrology >Komsomolskaya diamondiferous eclogites: evidence for oceanic crustal protoliths
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Komsomolskaya diamondiferous eclogites: evidence for oceanic crustal protoliths

机译：Komsomolskaya含钻石的榴辉岩：海洋地壳原生岩的证据

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The Komsomolskaya kimberlite is one of numerous (>l,000) kimberlite pipes that host eclogite xenoliths on the Siberian craton. Eclogite xenoliths from the adjacent Udachnaya kimberlite pipe have previously been geochemically well characterized; however, data from surrounding diamond-bearing kimberlite pipes from the center of the craton are relatively sparse. Here, we report major- and trace-element data, as well as oxygen isotope systematics, for mineral separates of diamondiferous eclogite xenoliths from the Komsomolskaya kimberlite, suggesting two distinct subgroups of a metamorphosed, subducted oceanic crustal protolith. Using almandine contents, this suite can be divided into two subgroups: group B1, with a high almandine component (>20 mol%) and group B2, with a low almandine component (<20 mol%). Reconstructed REE profiles for B1 eclogites overlap with typical oceanic basalts and lack distinct Eu anomalies. In addition, elevated oxygen isotope values, which are interpreted to reflect isotopic exchange with seawater at low temperatures (<350 °C), are consistent with an upper-oceanic crustal protolith. Reconstructed REE profiles for B2 eclogites are consistent with oceanic gabbros and display distinct Eu anomalies, suggesting a plagioclase-rich cumulate protolith. In contrast to B1, B2 eclogites do not display elevated oxygen isotope values, suggesting an origin deep within the crustal pile, where little-to-no interaction with hydrothermal fluids has occurred. Major-element systematics were reconstructed based on mineral modes; group B1. eclogites have higher MgO wt% and lower SiO_2 wt%, with respect to typical oceanic basalts, reflecting a partial melting event during slab subduction. Calculated residues from batch partial melt modeling of a range of Precambrian basalts overlap with group Bl trace-element chemistry. When taken together with the respective partial melt trajectories, these melting events are clearly linked to the formation of Tonalite-Trondhjemite-Granodiorite (TTG) complexes. As a result, we propose that many, if not all, diamondiferous eclogite xenoliths from Komsomolskaya represent mantle 'restites' that preserve chemical signatures of Precambrian oceanic crust.
机译：Komsomolskaya金伯利岩是众多（> l，000）金伯利岩管道之一，在西伯利亚克拉通上盛有榴辉岩异岩。相邻的Udachnaya金伯利岩管的榴辉岩异岩在地球化学上已得到很好的表征。但是，来自克拉通中心的含钻石的金伯利岩管道周围的数据相对稀疏。在这里，我们报告了来自Komsomolskaya金伯利岩的菱铁矿榴辉岩异岩的矿物分离物中的主要元素和痕量元素数据，以及氧同位素系统，表明了变质，俯冲的海洋地壳原生岩的两个不同的亚组。使用铝金刚烷含量，该套件可分为两个亚组：铝金刚烷含量高（> 20 mol％）的B1组和铝金刚烷含量低（<20 mol％）的B2组。 B1榴辉岩的重构REE剖面与典型的海洋玄武岩重叠，并且缺乏明显的Eu异常。另外，升高的氧同位素值被解释为反映了在低温（<350°C）下与海水的同位素交换，这与上洋壳地壳原岩一致。 B2榴辉岩的重构REE剖面与海洋辉长岩一致，并表现出明显的Eu异常，表明富含斜长石的累积原生石。与B1相比，B2榴辉岩没有显示出较高的氧同位素值，表明其起源于地壳深处，与热液几乎没有相互作用。基于矿物模式重建了主要元素系统; B1组。与典型的海洋玄武岩相比，榴辉岩的MgO含量较高，而SiO_2含量较低，反映了板坯俯冲过程中的部分熔融事件。从一系列前寒武纪玄武岩的部分熔融模型中计算出的残留物与B1组微量元素化学重叠。当与各自的部分熔体轨迹一起考虑时，这些熔解事件与Tonalite-Trondhjemite-Granodiorite（TTG）配合物的形成明显相关。结果，我们建议，如果不是全部的话，那么来自Komsomolskaya的菱形榴辉岩异辉石代表着地幔“重辉石”，它们保留了前寒武纪大洋壳的化学特征。

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