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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Gas geochemistry of the magmatic-hydrothermal fluid reservoir in the Copahue-Caviahue Volcanic Complex (Argentina)
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Gas geochemistry of the magmatic-hydrothermal fluid reservoir in the Copahue-Caviahue Volcanic Complex (Argentina)

机译：Copahue-Caviahue火山综合体（阿根廷）岩浆热液储层的天然气地球化学

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摘要

Copahue volcano is part of the Caviahue-Copahue Volcanic Complex (CCVC), which is located in the southwestern sector of the Caviahue volcano-tectonic depression (Argentina-Chile). This depression is a pull-apart basin accommodating stresses between the southern Liquine-Ofqui strike slip and the northern Copahue-Antinir compressive fault systems, in a back-arc setting with respect to the Southern Andean Volcanic Zone. In this study, we present chemical (inorganic and organic) and isotope compositions (δ~(13)C-CO_2, δ~(15)N, ~3He/~4He, ~(40)Ar/~(36)Ar, δ~(13)C-CH_4, 8D-CH_4, and 8D-H_2O and δ~(18)O-H_2O) of fumaroles and bubbling gases of thermal springs located at the foot of Copahue volcano sampled in 2006, 2007 and 2012. Helium isotope ratios, the highest observed for a Southern American volcano (R/R_a up to 7.94), indicate a non-classic arc-like setting, but rather an extensional regime subdued to asthenospheric thinning. δ~(13)C-CO_2 values (from -8.8‰ to -6.8‰ vs. V-PDB), δ~(15)N values ( + 5.3‰ to +5.5‰ vs. Air) and CO_2/~3He ratios (from 1.4 to 8.8 × 10~9) suggest that the magmatic source is significantly affected by contamination of subducted sediments. Gases discharged from the northern sector of the CCVC show contribution of ~3He-poor fluids likely permeating through local fault systems. Despite the clear mantle isotope signature in the CCVC gases, the acidic gas species have suffered scrubbing processes by a hydrothermal system mainly recharged by meteoric water. Gas geothermometry in the H_2O-CO_2-CH_4-CO-H_2 system suggests that CO and H_2 re-equilibrate in a separated vapor phase at 200°-220 ℃. On the contrary, rock-fluid interactions controlling CO_2, CH_4 production from Sabatier reaction and C_3H_8 dehydrogenation seem to occur within the hydrothermal reservoir at temperatures ranging from 250° to 300 ℃. Fumarole gases sampled in 2006-2007 show relatively low N_2/He and N_2/Ar ratios and high R/R_a values with respect to those measured in 2012. Such compositional and isotope variations were likely related to injection of mafic magma that likely triggered the 2000 eruption. Therefore, changes affecting the magmatic system had a delayed effect on the chemistry of the CCVC gases due to the presence of the hydrothermal reservoir. However, geochemical monitoring activities mainly focused on the behavior of inert gas compounds (N_2 and He), should be increased to investigate the mechanism at the origin of the unrest started in 2011.
机译：Copahue火山是Caviahue-Copahue火山综合体（CCVC）的一部分，该综合体位于Caviahue火山-构造depression陷（阿根廷-智利）的西南地区。该凹陷是在南部安第斯火山带的后弧环境中，在南部Liquine-Ofqui滑动带与北部Copahue-Antinir压缩断层系统之间承受应力的拉开盆地。在这项研究中，我们介绍了化学（无机和有机）和同位素组成（δ〜（13）C-CO_2，δ〜（15）N，〜3He /〜4He，〜（40）Ar /〜（36）Ar， 2006年，2007年和2012年采样的位于Copahue火山脚下的喷气孔和温泉冒泡气体的δ〜（13）C-CH_4、8D-CH_4和8D-H_2O和δ〜（18）O-H_2O）。氦同位素比率是南美火山观测到的最高比率（R / R_a最高为7.94），表明它是非经典的弧状环境，但是却导致了软流圈变薄的扩张机制。 δ〜（13）C-CO_2值（相对于V-PDB为-8.8‰至-6.8‰），δ〜（15）N值（相对于空气为+ 5.3‰至+ 5.5‰）和CO_2 /〜3He比（从1.4到8.8×10〜9）表明岩浆源受到俯冲沉积物污染的显着影响。从CCVC北部地区排出的气体显示出约3He贫化流体的贡献，这些流体很可能会渗透到局部断层系统中。尽管CCVC气体中有明显的地幔同位素特征，但酸性气体种类仍受到主要由陨石水补给的热液系统的洗涤过程。 H_2O-CO_2-CH_4-CO-H_2系统中的气体地热法表明，CO和H_2在分离的气相中在200°-220℃时重新平衡。相反，在温度为250°至300℃的热液储层中，似乎发生了控制CO_2，Sabatier反应生成CH_4和C_3H_8脱氢的流体相互作用。与2012年测得的相比，在2006-2007年采样的富马ole气体显示出相对较低的N_2 / He和N_2 / Ar比，以及较高的R / R_a值。这种成分和同位素变化可能与注入镁铁质岩浆有关，可能触发了2000年喷发。因此，由于水热储层的存在，影响岩浆系统的变化对CCVC气体的化学反应具有延迟的影响。但是，应增加主要针对惰性气体化合物（N_2和He）行为的地球化学监测活动，以调查始于2011年的动乱起源的机理。

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    M. Agusto; F.Tassi; A.T. Caselli; O. Vaselli; D. Rouwet; B. Capaccioni; S. Caliro; G. Chiodini; T. Darrah;

  • 作者单位

    IDEAN-GESVA Dpto. Cs. Geologicas, FCEN, Universidad de Buenos Aires, Ciudad Universitaria, Pab.2, 1428, Buenos Aires, Argentina;

    Department of Earth Sciences, University of Florence, Via La Pira, 4, 50121, Florence, Italy,Institute of Geosciences and Earth Resources of the National Research Council (CNR-IGG), Via La Pira, 4, 50121, Florence, Italy;

    IDEAN-GESVA Dpto. Cs. Geologicas, FCEN, Universidad de Buenos Aires, Ciudad Universitaria, Pab.2, 1428, Buenos Aires, Argentina;

    Department of Earth Sciences, University of Florence, Via La Pira, 4, 50121, Florence, Italy,Institute of Geosciences and Earth Resources of the National Research Council (CNR-IGG), Via La Pira, 4, 50121, Florence, Italy;

    Istituto Nazionale Geofisica e Vuclanologia, Sezione di Bologna, Via Donato Creti 12,40128, Bologna, Italy;

    Department of Earth and Geological-Environmental Sciences, Piazza Porta San Donato, 1, 40126, Bologna, Italy;

    Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano, Naples, Italy;

    Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano, Naples, Italy;

    Division of Earth and Ocean Sciences, Nicholas School of the Environment, Duke University, Durham, NC 27708, USA;

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  • 正文语种 eng
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  • 关键词

    Fluid geochemistry; Copahue volcano; Fumarolic fluid; Hydrothermal reservoir; Volcanic unrest;

    机译：流体地球化学;科帕韦火山;富马酰流体;热液储层;火山动荡;

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