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首页> 外文期刊>Contributions to Mineralogy and Petrology >Halogens and noble gases in Mathematician Ridge meta-gabbros, NE Pacific: implications for oceanic hydrothermal root zones and global volatile cycles
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Halogens and noble gases in Mathematician Ridge meta-gabbros, NE Pacific: implications for oceanic hydrothermal root zones and global volatile cycles

机译：东北太平洋太平洋数学家山脊超长三角的卤素和稀有气体：对海洋热液根区和全球挥发性循环的影响

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摘要

Six variably amphibolitised meta-gabbros cut by quartz-epidote veins containing high-salinity brine, and vapour fluid inclusions were investigated for halogen (Cl, Br, I) and noble gas (He, Ne, Ar, Kr, Xe) concentrations. The primary aims were to investigate fluid sources and interactions in hydrothermal root zones and determine the concentrations and behaviours of these elements in altered oceanic crust, which is poorly known, but has important implications for global volatile (re) cycling. Amphiboles in each sample have average concentrations of 0.1-0.5 wt% Cl, 0.5-3 ppm Br and 5-68 ppb I. Amphibole has Br/Cl of similar to 0.0004 that is about ten times lower than coexisting fluid inclusions and seawater, and I/Cl of 2-44 x 10(-6) that is 3-5 times lower than coexisting fluid inclusions but higher than seawater. The amphibole and fluid compositions are attributed to mixing halogens introduced by seawater with a large halogen component remobilised from mafic lithologies in the crust and fractionation of halogens between fluids and metamorphic amphibole formed at low water-rock ratios. The metamorphic amphibole and hydrothermal quartz are dominated by seawater-derived atmospheric Ne, Ar, Kr and Xe and mantle-derived He, with He-3/He-4 of similar to 9 R/Ra (Ra = atmospheric ratio). The amphibole and quartz preserve high He-4 concentrations that are similar to MORB glasses and have noble gas abundance ratios with high He-4/Ar-36 and Ne-22/Ar-36 that are greater than seawater and air. These characteristics result from the high solubility of light noble gases in amphibole and suggest that all the noble gases can behave similarly to 'excess Ar-40' in metamorphic hydrothermal root zones. All noble gases are therefore trapped in hydrous minerals to some extent and can be inefficiently lost during metamorphism implying that even the lightest noble gases (He and Ne) can potentially be subducted into the Earth's mantle.
机译：研究了六种不同的两性变质辉长石，它们由含有高盐度盐水的石英埃皮科德脉和切割的蒸气流体包裹体研究了卤素（Cl，Br，I）和稀有气体（He，Ne，Ar，Kr，Xe）的浓度。主要目的是研究热液根区中的流体来源及其相互作用，并确定这些元素在改变的洋壳中的浓度和行为，这鲜为人知，但对全球挥发性（再）循环具有重要意义。每个样品中的闪石的平均浓度为0.1-0.5 wt％Cl，0.5-3 ppm Br和5-68 ppbI。闪石的Br / Cl约为0.0004，比共存的流体包裹体和海水低约十倍，并且I / Cl为2-44 x 10（-6），比共存的流体包裹体低3-5倍，但比海水高。闪石和流体的成分归因于将海水引入的卤素与从镁铁质岩性中移出的大卤素组分混合在一起，并在流体和低水-岩比的变质闪石之间分馏了卤素。变质的闪石和热液石英被海水中的大气Ne，Ar，Kr和Xe以及地幔中的He所控制，He-3 / He-4接近9 R / Ra（Ra =大气比）。闪石和石英保存的高He-4浓度类似于MORB玻璃，并具有高的惰性气体丰度比，而高He-4 / Ar-36和Ne-22 / Ar-36大于海水和空气。这些特性是由于稀有稀有气体在闪石中的高度溶解性所致，并表明所有稀有气体在变质热液根区的行为都类似于“过量Ar-40”。因此，所有稀有气体在一定程度上都被困在含水矿物中，并且在变质过程中会被低效率地损失掉，这意味着即使最轻的稀有气体（He和Ne）也有可能被俯冲到地幔中。

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