加拿大维多利亚大学 R.A. Morris 近日的研究揭示，岩浆-碳酸盐岩相互作用能驱动火山弧处浅层岩脉和岩床中CO₂的产生和金属富集。该项研究成果发表在2023年12月7日出版的《地质学》上。

为了更好地了解弧岩浆中 CO₂ 产生的作用和机制，团队成员详细的研究了加拿大温哥华岛侏罗纪富矿带中玄武岩岩脉和与碳酸盐的储层接触关系。研究发现沿岩脉和岩基边缘形成的离散边界熔体与石灰岩接触，显示出独特的 Ca、U、Sr 富集；Si 亏缺和与主石灰岩接近的 ⁸⁷Sr/⁸⁶Sr 值(约 0.708)。

二元混合模型表明，约 20 %-25 % 的石灰岩同化成玄武岩，形成边界熔体。边界和内部熔体之间的不同粘度阻碍了混合和化学均质化，但似乎促进了上坡扩散和在几分钟到几天内冷却的系统内的金属富集。虽然浅岩脉和岩基在岛弧岩浆系统中的体积可能较小，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—碳酸盐岩的相互作用，最终可能比更常见和体积更大的岩体产生更多的 CO₂。

据悉，来自地壳碳酸盐岩的 CO₂ 对弧岩浆的贡献及其在长期碳循环中的作用一直存在争议。

附：英文原文

Title: Magma-carbonate interactions drive CO₂ production and metal enrichment in shallow dikes and sills at volcanic arcs

Author: R.A. Morris, D. Canil, J. Spence

Issue&Volume: 2023-12-07

Abstract: 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.

DOI: 10.1130/G51439.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G51439.1/630495/Magma-carbonate-interactions-drive-CO2-productionredirectedFrom=fulltext