Ankaramites, which are clinopyroxene-rich basalts with primitive whole-rock compositions (Mg# >65), are common in oceanic arcs and are characterized by high whole-rock CaO/AlO (>1.0) ratios and olivine crystals with anomalously low nickel contents (<0.2 wt% NiO). These geochemical characteristics cannot be explained by the melting of ordinary mantle peridotite. However, their origin is critical for understanding the formation of primary magmas in oceanic arcs. Here, we investigated olivine-hosted melt inclusions (MIs) from ankaramites and magnesian andesites of the Kibblewhite Volcano in the Kermadec arc. The MIs from the ankaramites have similar major and trace element characteristics to the host rocks, indicating that the ankaramites did not result from an accumulation of mafic minerals but rather represent the primary magma in the Kibblewhite Volcano. The MIs from the magnesian andesites were hosted in forsteritic olivine xenocrysts with a wide range of NiO contents (Fo; 0.13–0.39 wt% NiO) and have similar major element compositions to the ankaramites but exhibit a wide range of CaO/AlO (0.85–1.54). The trace element characteristics of the MIs from the magnesian andesites do not match those of the host rocks, indicating that they are not primary melts of the magnesian andesites but primitive basaltic melts generated before the magnesian andesites formed.

中文翻译：

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为什么大洋弧玄武岩富钙贫镍？来自克马德克岛弧基布尔怀特火山的橄榄石熔融包裹体的见解


安卡拉岩是一种富含单斜辉石的玄武岩，具有原始的全岩成分（Mg#>65），常见于大洋弧，其特点是全岩 CaO/Al2O 比率高（>1.0）和镍含量异常低的橄榄石晶体（<0.2 wt% NiO）。这些地球化学特征无法用普通地幔橄榄岩的熔化来解释。然而，它们的起源对于理解大洋弧中原生岩浆的形成至关重要。在这里，我们研究了来自克马德克岛弧基布尔怀特火山的安卡拉岩和镁质安山岩的橄榄石熔融包裹体 (MI)。安卡拉岩的 MI 与主岩具有相似的主量和微量元素特征，表明安卡拉岩不是镁铁质矿物堆积的结果，而是代表基布尔怀特火山的原生岩浆。镁质安山岩中的 MI 存在于镁橄榄石橄榄石中，其 NiO 含量范围广泛（Fo；0.13–0.39 wt% NiO），并且与安卡拉岩具有相似的主要元素组成，但表现出广泛的 CaO/Al2O 范围（0.85– 1.54）。镁质安山岩中的MIs的微量元素特征与母岩不符，表明它们不是镁质安山岩的原生熔体，而是镁质安山岩形成之前产生的原始玄武岩熔体。