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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Prodigious emission rates and magma degassing budget of major, trace and radioactive volatile species from Ambrym basaltic volcano, Vanuatu island Arc
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Prodigious emission rates and magma degassing budget of major, trace and radioactive volatile species from Ambrym basaltic volcano, Vanuatu island Arc

机译：瓦努阿图岛弧段安布林玄武岩火山的主要，痕量和放射性挥发性物种的巨大排放速率和岩浆脱气预算

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摘要

Ambrym volcano, in the Vanuatu arc, is one of the most active volcanoes of the Southwest Pacific region, where persistent lava lake and/or Strombolian activity sustains voluminous gas plume emissions. Here we report on the first comprehensive budget for the discharge of major, minor, trace and radioactive volatile species from Ambrym volcano, as well as the first data for volatiles dissolved in its basaltic magma (olivine-hosted melt inclusions). In situ MultiGAS analysis of H2O, CO2, SO2 and H2S in crater rim emissions, coupled with filter-pack determination of SO2, halogens, stable and radioactive metals demonstrates a common magmatic source for volcanic gases emitted by its two main active craters, Benbow and Marum. These share a high water content (similar to 93 mol%), similar S/Cl, Cl/ F, Br/Cl molar ratios, similar (Po-210/Pb-210) and (Bi-210/(210P)b) activity ratios, as well as comparable proportions in most trace metals. Their difference in CO2/SO2 ratio (1.0 and 5.6-3.0, respectively) is attributed to deeper gas melt separation at Marum (Strombolian explosions) than Benbow (lava lake degassing) during our measurements in 2007. Airborne UV sensing of the SO2 plume flux (90 kg s(-1) or 7800 tons d(-1)) demonstrates a prevalent degassing contribution (similar to 65%) of Benbow crater in that period and allows us to quantify the total volatile fluxes during medium-level eruptive activity of the volcano. Results reveal that Ambrym ranks among the most powerful volcanic gas emitters on Earth, producing between 5% and 9% of current estimates for global subaerial volcanic emissions of H2O, CO2, HCl, Cu, Cr, Cd, Au, Cs and Tl, between 10% and 17% of SO2, HF, HBr, Hg, Po-210 and Pb-210, and over 30% of Ag, Se and Sn. Global flux estimates thus need to integrate its contribution and be revised accordingly. Prodigious gas emission from Ambrym does not result from an anomalous volatile enrichment nor a differential excess degassing of its feeding basalt: this latter contains relatively modest dissolved amounts of H2O(<= 1.3 wt%), CO2 (similar to 0.10 wt%), S (0.075 wt%) and Cl (0.05 wt%), and its degassing under prevalent closed-system conditions well reproduces the composition of emitted volcanic gases. Instead, we show that the gas discharge is sustained by a very high basalt supply rate of 25 m(3) s(-1), from a large (similar to 0.5 km(3)) magma reservoir probably emplaced at similar to 3.8 km depth below the summit caldera according to both the H2O-CO2 content of bubble-free melt inclusions and preliminary seismic data. Radioactive disequilibria in the volcanic gases constrain that this reservoir may be entirely renewed in about 240 days. The comparatively low magma extrusion rate requires extensive convective overturn of the basaltic magma column and recycling of the unerupted (denser) degassed magma in the plumbing system, in agreement with textural features of erupted products. Finally, our results suggest that the Indian MORB-type mantle source of Ambrym basalts is modestly enriched in slab-derived water and other volatiles, in agreement with the prevalent volcanodastic nature of subducted sediments and their lower subduction rate under the central Vanuatu arc due to its collision with the D'Enfrecasteaux Ridge. (C) 2015 Elsevier B.V. All rights reserved.
机译：瓦努阿图弧段的安布林火山是西南太平洋地区最活跃的火山之一，在那里持续的熔岩湖和/或斯特伦伯利亚活动维持着大量的烟羽排放。在这里，我们报告了有关从Ambrym火山排放主要，次要，痕量和放射性挥发性物质的第一个综合预算，以及溶解在其玄武岩浆（橄榄石包裹的熔体包裹体）中的挥发性物质的第一个数据。对陨石坑边缘排放物中的H2O，CO2，SO2和H2S进行原位MultiGAS分析，并通过过滤器测定SO2，卤素，稳定和放射性金属，证明了由其两个主要活性陨石坑Benbow和妈它们具有较高的水含量（约93 mol％），相似的S / Cl，Cl / F，Br / Cl摩尔比，相似的（Po-210 / Pb-210）和（Bi-210 /（210P）b）活性比，以及大多数痕量金属中的可比比例。他们在CO2 / SO2比率上的差异（分别为1.0和5.6-3.0）是由于我们在2007年的测量中，在Marum（Strombolian爆炸）处的气体熔体分离比Benbow（熔岩湖脱气）更深。空气中的SO2羽流通量感测（90千克s（-1）或7800吨d（-1））证明了Benbow火山口在该时期的普遍脱气作用（约占65％），使我们能够定量地估算该火山口在中等水平的喷发活动中的总挥发通量。火山。结果表明，Ambrym跻身于地球上最强大的火山气体排放国之列，在当前估计的全球海底火山气中H2O，CO2，HCl，Cu，Cr，Cd，Au，Cs和Tl排放量中占5％至9％。 SO2，HF，HBr，Hg，Po-210和Pb-210分别占10％和17％，Ag，Se和Sn占30％以上。因此，全球通量估计需要整合其贡献并相应地进行修订。来自Ambrym的大量气体排放既不是由于其异常的挥发富集也不是其玄武岩的过量脱气而造成的：该玄武岩中含有相对适量的H2O（<= 1.3 wt％），CO2（约0.10 wt％），S （0.075 wt％）和Cl（0.05 wt％），以及在普遍的封闭系统条件下进行脱气可以很好地重现所散发的火山气体成分。取而代之的是，我们显示了一个巨大的玄武岩供应速率（25 m（3）s（-1））从一个大型（约0.5 km（3））的岩浆储层中维持了天然气的排放，该岩浆储层可能位于约3.8 km根据无气泡熔体夹杂物的H2O-CO2含量和初步地震数据，确定火山口下方的深度。火山气体中的放射性失衡限制了该储层可能在约240天之内全部更新。相对较低的岩浆挤出速率，需要玄武岩浆柱进​​行广泛的对流翻转，并在管道系统中回收未喷出（浓密）脱气岩浆，这与喷出产品的质地特征相符。最后，我们的结果表明，印度的MORB型Ambrym玄武岩地幔源在一定程度上富含了平板状水和其他挥发物，这与俯冲沉积物的普遍火山岩性及其在瓦努阿图弧中部的俯冲率较低有关。与D'Enfrecasteaux Ridge的碰撞。 （C）2015 Elsevier B.V.保留所有权利。

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