Interactions between carbonated ultramafic silicate magmas and the continental lithospheric mantle results in the formation of dunite—a ubiquitous xenolith type in kimberlites and aillikites. However, whether this process dominantly occurs in the mantle source region or by subsequent interactions between lithospheric mantle fragments and transporting silica-undersaturated magmas during ascent remains debated. Aillikite magmas, which are derived from the fusion of carbonate-phlogopite metasomes under diamond-stability field upper mantle conditions, have a mineralogically more complex source than kimberlites, providing an opportunity to more fully constrain the origin of dunite xenoliths in such deeply sourced carbonated silicate magmas. Here we present a major and trace element study of olivine occurring in xenoliths and as phenocrysts in an aillikite dike located on the southern Superior Craton. We show that olivine within the dunite microxenoliths exhibits extreme enrichment in Al, Cr, Na, and V when compared to equivalent xenoliths carried by kimberlites. We interpret these results as evidence for the presence of carbonate-phlogopite metasomes left residual in the cratonic mantle source during aillikite magma formation. Our results are inconsistent with models of dunite formation through orthopyroxene dissolution upon kimberlite/aillikite magma ascent, supporting an origin for such dunites that is more closely linked to primary melt generation at the base of relatively thick continental lithosphere. Our work demonstrates that it is possible to constrain the precursor composition of cratonic mantle dunite at depth, thereby facilitating the further exploration of how carbonated silicate magmas modify and weaken continental lithospheric roots.

中文翻译：

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碳酸化硅酸盐熔体相互作用对地幔橄榄石的影响

碳酸化超镁铁质硅酸盐岩浆与大陆岩石圈地幔之间的相互作用导致了纯长岩的形成——金伯利岩和铝镁石中普遍存在的捕虏体类型。然而，这一过程是主要发生在地幔源区还是由岩石圈地幔碎片与上升过程中输送的二氧化硅不饱和岩浆之间的后续相互作用引起的，仍有争议。在金刚石稳定场上地幔条件下，源自碳酸盐-金云母交代体融合的异镁石岩浆在矿物学上比金伯利岩更复杂，这为更全面地限制这种来源深厚的碳酸盐硅酸盐中纯晶包体的起源提供了机会岩浆。在这里，我们对存在于捕虏体中的橄榄石和作为位于苏必利尔克拉通南部的埃利石岩脉中的斑晶进行了主要和微量元素研究。我们表明，与金伯利岩携带的等效捕虏体相比，纯质微捕体中的橄榄石在 Al、Cr、Na 和 V 中表现出极大的富集。我们将这些结果解释为在岩浆形成过程中存在残留在克拉通地幔源中的碳酸盐-金云母交代体的证据。我们的结果与通过金伯利岩 / 硅铝石岩浆上升时的斜方辉石溶解形成的单质岩形成模型不一致，支持这种纯质岩的起源与相对厚的大陆岩石圈底部的初级熔体生成更密切相关。