The dearth of cumulate magmatic roots in accretionary orogens is a cornerstone of models that postulate redistribution of mass and energy within the crust for the genesis of intermediate to silicic magmatism. Likewise, the origin of the evolved Acadian (Devonian) plutonism in the New England Appalachians (northeastern USA) has long been explained by closed-system crustal melting due to the absence of associated coeval deep mafic counterparts. Here, we report the discovery of Acadian hydrous ultramafic cumulate rocks that formed by deep-seated (∼1.1 GPa) fractional crystallization processes from a mantle-derived parental melt (Connecticut, southern New England, USA). These rocks are the first of their kind identified in the Appalachian orogen, and one of only a handful of preserved deep subarc hydrous cumulates worldwide. We propose a genetic link between the studied rocks and the evolved coeval plutonism in central-southern New England, where the former represent the missing deep cumulate roots of the same magmatic arc. Our findings support the hypothesis that differentiation of mantle-derived hydrous magmas by fractional crystallization and assimilation processes in the deep crust is a fundamental process in the production of intermediate to silicic magmatism and the geochemical evolution of the continental crust.

中文翻译：

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北美洲东部阿卡迪造山带的深岩浆累积根

增生造山带中堆积的岩浆根的缺乏是模型的基石，该模型假定地壳内质量和能量的重新分布是硅质岩浆作用的中间成因。同样地，由于缺乏相关的近代深基性镁铁质对应物，封闭系统地壳融化长期以来一直解释了新英格兰阿巴拉契亚人（美国东北部）演化的阿卡迪亚（德文尼亚）岩体的起源。在这里，我们报告了由地幔衍生的母体熔体（康涅狄格州，新英格兰南部，美国）的深层（约1.1 GPa）分级结晶过程形成的阿卡迪亚含水超镁铁质堆积岩的发现。这些岩石是阿巴拉契亚造山带中发现的同类岩石中的第一种，并且是全球少数少数保存完好的深弧含水层之一。我们提出了新英格兰中南部地区研究的岩石与演化的古代冥想关系之间的遗传联系，其中前者代表了同一岩浆弧缺失的深累积根。我们的发现支持以下假说：深部地壳中的部分结晶和同化作用使地幔源性含水岩浆分化是生产中，硅质岩浆作用和大陆壳地球化学演化的基本过程。