Halogens and noble gases in Mathematician Ridge meta-gabbros, NE Pacific: implications for oceanic hydrothermal root zones and global volatile cycles
Halogens and noble gases in Mathematician Ridge meta-gabbros, NE Pacific: implications for oceanic hydrothermal root zones and global volatile cycles
复制标题
东北太平洋数学家岭变辉长岩中的卤素和稀有气体：对海洋热液根区和全球挥发性循环的影响
DOI：
10.1007/s00410-015-1192-x
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发表时间：
2015
影响因子：
3.5
通讯作者：
["M. Kendrick
中科院分区：
文献类型：
--
作者：
["M. Kendrick
研究了6个被含高盐度卤水的石英绿帘石脉切割的角闪变辉长岩和气相流体包裹体中卤素（Cl，Br，I）和稀有气体（He，Ne，Ar，Kr，Ar）的含量。主要目的是调查热液根区的流体来源和相互作用，并确定这些元素在蚀变洋壳中的浓度和行为，这一点鲜为人知，但对全球挥发性（再）循环具有重要影响。每个样品中的角闪石具有0.1-0.5重量% Cl、0.5-3 ppm Br和5-68 ppb I的平均浓度。角闪石的Br/Cl值约为0.0004，比共存的流体包裹体和海水低约10倍; I/Cl值为2-44 × 10− 6，比共存的流体包裹体低3-5倍，但比海水高。角闪石和流体的组成是由于混合卤素引入海水与大量的卤素组分在地壳中的镁铁质岩性和分馏的卤素之间的流体和变质角闪石形成在低水岩比。变质角闪石和热液石英主要由海水来源的大气Ne、Ar、Kr、Ar和幔源He组成，3 He/4 He为~9 R/Ra（Ra =大气比值）。角闪石和石英保存了类似于MORB玻璃的高4 He浓度，并具有高于海水和空气的高4 He/36 Ar和22 Ne/36 Ar的稀有气体丰度比。这些特征是由于角闪石中轻稀有气体的高溶解度所致，并表明在变质热液根带中，所有稀有气体都具有类似于“过剩40 Ar”的行为。因此，所有的稀有气体在某种程度上都被困在含水矿物中，并且在变质过程中可能无效地损失，这意味着即使是最轻的稀有气体（He和Ne）也可能被俯冲到地幔中。
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 ~0.0004 that is about ten times lower than coexisting fluid inclusions and seawater, and I/Cl of 2–44 × 10−6that 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, with3He/4He of ~9 R/Ra (Ra = atmospheric ratio). The amphibole and quartz preserve high4He concentrations that are similar to MORB glasses and have noble gas abundance ratios with high4He/36Ar and22Ne/36Ar 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 ‘excess40Ar’ 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.