The contribution of CO2 from crustal carbonates into arc magmas is debated, as is its role in the long-term C cycle. To better understand the contributions and mechanisms that drive CO2 production in arc magmas, we examined in detail basaltic dike and sill contacts with carbonate in the Jurassic Bonanza arc on Vancouver Island, Canada. We discovered discrete boundary melts that formed along dike and sill margins in contact with limestone, which display unique Ca, U, and Sr enrichments, Si depletion, and 87Sr/86Sr that approaches host limestone values (~0.708). Binary mixing modeling indicates ~20%–25% limestone assimilation into basalt formed the boundary melts. Contrasting viscosities between boundary and interior melts hinder mixing and chemical homogenization but appear to promote uphill diffusion and metal enrichment within systems that cool in minutes to days. While shallow dikes and sills may be volumetrically minor in an arc magma system, the open flow of magma and large surface area in channels greatly enhances magma-carbonate interactions, and ultimately CO2 production, likely over that of more common and voluminous plutons.

中文翻译：

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岩浆-碳酸盐相互作用促进火山弧浅岩脉和岩床中二氧化碳的产生和金属富集

地壳碳酸盐中的二氧化碳对弧岩浆的贡献存在争议，其在长期碳循环中的作用也存在争议。为了更好地了解弧岩浆中二氧化碳产生的贡献和机制，我们详细研究了加拿大温哥华岛侏罗纪富矿弧中玄武岩岩脉和岩床与碳酸盐的接触。我们发现了沿着与石灰岩接触的岩脉和岩台边缘形成的离散边界熔体，这些熔体表现出独特的 Ca、U 和 Sr 富集、Si 贫化以及接近宿主石灰石值 (~0.708) 的 87Sr/86Sr。二元混合模型表明，约 20%–25% 的石灰石同化为玄武岩，形成了边界熔体。边界和内部熔体之间的对比粘度阻碍了混合和化学均质化，但似乎促进了在几分钟到几天内冷却的系统内的上坡扩散和金属富集。虽然在弧岩浆系统中，浅岩脉和岩台的体积可能较小，但岩浆的开放流动和通道中的大表面积极大地增强了岩浆-碳酸盐的相互作用，并最终增强了二氧化碳的产生，可能超过了更常见和体积更大的岩体。