Abundant carbon in the mantle beneath Hawai'i
Abundant carbon in the mantle beneath Hawai'i
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DOI：
10.1038/ngeo3007
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发表时间：
2017-09-01
影响因子：
18.3
通讯作者：
Poland, Michael P.
中科院分区：
文献类型：
--
作者：
Anderson, Kyle R.;Poland, Michael P.
对地幔中碳浓度的估计相差超过一个数量级，阻碍了我们了解地幔结构和矿物学、部分熔融和碳循环的能力。供应热点海洋岛屿火山的地幔岩浆中的二氧化碳浓度对地幔碳产生了最直接的限制，但在上升过程中被脱气广泛修改。在这里，我们展示了未脱气的岩浆和地幔碳浓度可以在贝叶斯框架下利用海洋岛屿火山的不同地质信息进行估计。我们对二氧化碳浓度的估计不依赖于复杂的脱气模型、地球化学示踪元素、假设的岩浆供应率或稀有的未脱气岩石样本。相反，我们将火山二氧化碳排放速率与可能的岩浆供应速率结合起来，后者是从岩浆储存和喷发速率间接获得的。我们估计，供应夏威夷活火山的地幔岩浆的二氧化碳含量为0.97(-0.19)(+0.25)wt%-约比之前认为的高40%-来自碳浓度为263(-62)(+81)ppm的地幔源区。我们的结果表明，地幔热柱和大洋岛玄武岩是富碳的。我们的数据还揭示了氦同位素丰度、二氧化碳/Nb比率，并可能意味着海洋岛屿火山的二氧化碳排放量更高。
Estimates of carbon concentrations in Earth's mantle vary over more than an order of magnitude, hindering our ability to understand mantle structure and mineralogy, partial melting, and the carbon cycle. CO2 concentrations in mantle-derived magmas supplying hotspot ocean island volcanoes yield our most direct constraints on mantle carbon, but are extensively modified by degassing during ascent. Here we show that undegassed magmatic and mantle carbon concentrations may be estimated in a Bayesian framework using diverse geologic information at an ocean island volcano. Our CO2 concentration estimates do not rely upon complex degassing models, geochemical tracer elements, assumed magma supply rates, or rare undegassed rock samples. Rather, we couple volcanic CO2 emission rates with probabilistic magma supply rates, which are obtained indirectly from magma storage and eruption rates. We estimate that the CO2 content of mantle-derived magma supplying Hawai`i's active volcanoes is 0.97(-0.19)(+0.25) wt%-roughly 40% higher than previously believed-and is supplied from a mantle source region with a carbon concentration of 263(-62)(+81) ppm. Our results suggest that mantle plumes and ocean island basalts are carbon-rich. Our data also shed light on helium isotope abundances, CO2/Nb ratios, and may imply higher CO2 emission rates from ocean island volcanoes.