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首页> 外文期刊>Journal of Volcanology and Geothermal Research2012V243-244NOCT,15 >Update on the fluid geochemistry monitoring time series for geothermal systems in Dominica, Lesser Antilles island arc: 2009-2017
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Update on the fluid geochemistry monitoring time series for geothermal systems in Dominica, Lesser Antilles island arc: 2009-2017

机译：小安地列斯群岛多米尼加的地热系统的流体地球化学监测时间序列更新：2009-2017

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摘要

With updated geochemical and isotopic compositions obtained over the period 2009 to 2017, this study presents revised fluid characterizations for the active volcanic-hydrothermal systems on the island of Dominica in the Lesser Antilles, which were first reported in 2011. Hydrothermal waters of Dominica cover a wide spectrum of pH, temperatures and chemical composition. The pH of the thermal waters ranges from acidic to neutral (pH values of 1-7.8) and the waters are predominantly Na-SO4 in character (Na = 14-2127 mg/L; SO4 = 1-1725 mg/L), likely formed as a result of dilution of acidic H2S-rich gases in near surface oxygenated groundwater, and have experienced limited water-rock interaction. The geochemical composition of the waters for most of the hydrothermal systems studied indicate no significant changes, with the exception of the Boiling Lake, which experienced a short (-6 week) episode of instability in November 2016 which appeared to be associated with a small mud-rich explosion. Unlike the last such event in December 2004, which was reported to be earthquake-triggered, this event is possibly the consequence of a moderate-sized landslide into the lake. The lake draining episodes have been accompanied by changes in composition between Na-SO4 and Na-Cl, which is attributed to hydrothermal fluid contributions from two different aquifers: a shallower acid-sulphate hydrothermal aquifer and a deeply-sourced brine aquifer.Reservoir temperatures determined by quartz geothermometers have not changed significantly over the monitoring period, suggesting steady-state degassing of the magma chambers. In two areas, temperatures have increased: Watten Waven (from 83-90 degrees C to 89-139 degrees C) and Sulphur Springs (from 145-152 degrees C to 93-243 degrees C). The elevated reservoir temperatures have affected the isotopic composition of the waters (delta O-18 = - 5.7 to 9.1%. and 6D = -8 to 20.5%.,), that reflect a dominantly meteoric source, with boiling/degassing and evaporation also playing an important role. The time series data suggests that some hydrothermal areas are experiencing increased steam evaporation over time whereas other waters are becoming more meteoric. The delta C-13(DIC) is decoupled from the deuterium and oxygen-18 isotopes and shows very little variation over time, but a broad range in values from -11 to +5%.The dominant process contributing to delta C-13(DIC) is degassing of primarily magmatic CO2, as exhibited by the bubbling pools. Hydrothermal streams have experienced mixing with biogenic CO2 sources, including plant respiration and methanogenesis. The slight variations observed from site to site are likely a consequence of fractional degassing of the magma chamber during exsolution of CO2. Over the sampling period 2014-2017, the temperatures and delta C-13 values do not change, which suggests a current steady-state of degassing. (C) 2019 Elsevier B.V. All rights reserved.
机译：借助2009年至2017年期间获得的最新地球化学和同位素组成，本研究介绍了小安的列斯群岛多米尼加岛上活跃的火山-热液系统的流体特征，该流体特征于2011年首次报道。多米尼加的热液覆盖了pH，温度和化学成分范围广。热水的pH值范围从酸性到中性（pH值为1-7.8），并且水质主要为Na-SO4（Na = 14-2127 mg / L； SO4 = 1-1725 mg / L）。由于在地表含氧地下水附近稀释了富含H2S的酸性气体而形成的，并且经历了有限的水-岩相互作用。所研究的大多数热液系统的水的地球化学组成均未表明有明显变化，沸腾湖除外，沸腾湖在2016年11月经历了短暂的（-6周）不稳定性事件，其中似乎与少量泥浆有关。爆炸。与上次发生在2004年12月的地震报告不同，据报道该地震是地震触发的，该事件可能是由于中等大小的滑坡进入湖中造成的。湖泊排泄事件伴随着Na-SO4和Na-Cl之间的成分变化，这归因于两种不同含水层的热液贡献：较浅的酸性硫酸盐热液含水层和深层盐水含水层。确定了储层温度在监测期间，石英地热仪的测量值没有显着变化，表明岩浆室的稳态脱气。在两个地区，温度上升了：瓦滕韦恩（Watten Waven）（从83-90摄氏度增加到89-139摄氏度）和硫磺泉（从145-152摄氏度增加到93-243摄氏度）。升高的储层温度影响了水的同位素组成（δO-18 =-5.7至9.1％。和6D = -8至20.5％。），这反映了主要是陨石源，沸腾/脱气和蒸发也起重要作用。时间序列数据表明，随着时间的流逝，一些热液地区的蒸汽蒸发量增加，而其他水域则变得越来越快。 δC-13（DIC）与氘和18氧同位素解耦，并且随时间变化很小，但其值范围从-11到+ 5％不等。如鼓泡池所示，DIC是对岩浆主要的CO2脱气。热液流经历了与生物二氧化碳源的混合，包括植物呼吸作用和甲烷生成。从一个站点到另一个站点观察到的细微变化可能是在释放CO2期间岩浆腔室部分脱气的结果。在2014-2017采样周期内，温度和C-13增量均未发生变化，这表明脱气当前处于稳态。 （C）2019 Elsevier B.V.保留所有权利。

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