Xu Jing-Yao, Giuliani Andrea, Li Qiu-Li, Lu Kai, Melgarejo Joan Carles, Griffin William L
State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, 100029, Beijing, China.
Innovation Academy for Earth Science, Chinese Academy of Sciences, 100029, Beijing, China.
Nat Commun. 2021 Nov 2;12(1):6295. doi: 10.1038/s41467-021-26668-z.
Oxygen isotope ratios in mantle-derived magmas that differ from typical mantle values are generally attributed to crustal contamination, deeply subducted crustal material in the mantle source or primordial heterogeneities. Here we provide an alternative view for the origin of light oxygen-isotope signatures in mantle-derived magmas using kimberlites, carbonate-rich magmas that assimilate mantle debris during ascent. Olivine grains in kimberlites are commonly zoned between a mantle-derived core and a magmatic rim, thus constraining the compositions of both mantle wall-rocks and melt phase. Secondary ion mass spectrometry (SIMS) analyses of olivine in worldwide kimberlites show a remarkable correlation between mean oxygen-isotope compositions of cores and rims from mantle-like O/O to lower 'crustal' values. This observation indicates that kimberlites entraining low-O/O olivine xenocrysts are modified by assimilation of low-O/O sub-continental lithospheric mantle material. Interaction with geochemically-enriched domains of the sub-continental lithospheric mantle can therefore be an important source of apparently 'crustal' signatures in mantle-derived magmas.
与典型地幔值不同的幔源岩浆中的氧同位素比值通常归因于地壳污染、地幔源区中深度俯冲的地壳物质或原始不均一性。在此，我们利用金伯利岩（一种在上升过程中同化地幔碎屑的富碳酸盐岩浆），对地幔源岩浆中轻氧同位素特征的起源提出了另一种观点。金伯利岩中的橄榄石颗粒通常在地幔源核心和岩浆边缘之间呈环带分布，从而限制了地幔围岩和熔体相的成分。对全球金伯利岩中橄榄石的二次离子质谱（SIMS）分析表明，核心和边缘的平均氧同位素组成之间存在显著相关性，从类似地幔的O/O到较低的“地壳”值。这一观察结果表明，携带低O/O橄榄石捕虏晶的金伯利岩通过同化低O/O的次大陆岩石圈地幔物质而发生了改变。因此，与次大陆岩石圈地幔的地球化学富集域相互作用可能是幔源岩浆中明显“地壳”特征的一个重要来源。
