Calcium isotopic evidence for the mantle sources of carbonatites
Calcium isotopic evidence for the mantle sources of carbonatites
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DOI：
10.1126/sciadv.aba3269
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发表时间：
2020-06-01
期刊：
影响因子：
13.6
通讯作者：
Day, James M. D.
中科院分区：
文献类型：
--
作者：
Amsellem, Elsa;Moynier, Frederic;Day, James M. D.
碳酸盐岩的起源--含有50%以上碳酸盐矿物的火成岩--以及它们是来自原始地幔来源还是来自地表物质的再循环，仍然存在争议。钙同位素有可能解决碳酸盐岩的成因问题，因为与地幔相比，海相碳酸盐岩富含较轻的钙同位素。本文报道了从30亿年前至今的74个陆相和洋相碳酸盐岩及其伴生硅酸盐岩的钙同位素组成，以及37个样品的0和C同位素比值。富钙、镁和铁的碳酸盐岩比玄武岩等地幔岩石的钙同位素更轻，属于古代海相碳酸盐岩的同位素轻钙范围。这一特征反映了源岩的组成，同位素很轻，与表面碳酸盐物质进入地幔的循环一致。
The origin of carbonatites-igneous rocks with more than 50% of carbonate minerals-and whether they originate from a primary mantle source or from recycling of surface materials are still debated. Calcium isotopes have the potential to resolve the origin of carbonatites, since marine carbonates are enriched in the lighter isotopes of Ca compared to the mantle. Here, we report the Ca isotopic compositions for 74 carbonatites and associated silicate rocks from continental and oceanic settings, spanning from 3 billion years ago to the present day, together with 0 and C isotopic ratios for 37 samples. Calcium-, Mg-, and Fe-rich carbonatites have isotopically lighter Ca than mantle-derived rocks such as basalts and fall within the range of isotopically light Ca from ancient marine carbonates. This signature reflects the composition of the source, which is isotopically light and is consistent with recycling of surface carbonate materials into the mantle.