Chlorine-rich amphibole in deep layered gabbros as evidence for brine/rock interaction in the lower oceanic crust: A case study from the Wadi Wariyah, Samail Ophiolite, Sultanate of Oman
Chlorine-rich amphibole in deep layered gabbros as evidence for brine/rock interaction in the lower oceanic crust: A case study from the Wadi Wariyah, Samail Ophiolite, Sultanate of Oman
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深层辉长岩中富含氯的角闪石作为下洋地壳中盐水/岩石相互作用的证据：阿曼苏丹国萨迈伊蛇绿岩干河谷的案例研究
DOI：
10.1016/j.lithos.2018.09.015
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发表时间：
2018
期刊：
影响因子：
3.5
通讯作者：
Currin A
中科院分区：
文献类型：
--
作者：
Currin A
在阿曼苏丹国Samail蛇绿岩深成部分，横切层状橄榄石辉长岩的热液脉和岩墙指向大洋地壳深部热液循环的发生，这些特征记录了岩石与高温海水衍生流体或盐水之间的相互作用。海水衍生流体的深度渗透至莫霍面过渡带上方100 m处，随后与寄主岩石相互作用，导致热液蚀变从麻粒岩相逐渐下降至绿片岩相条件。在这里，我们提出了一个研究的静脉和dykelets形成的热液相互作用切割层状辉长岩在瓦迪Wariyah，使用岩相学，显微分析，同位素和结构的方法。我们把重点放在角闪石，这表明了一个显着的组成变化，从高钛magnesiohastingsite和pargasite通过magnesiohornaltite和edenite，富Cl ferropargasite和hastingsite（高达1.5 a.p.f.u. Cl）和阳起石。这些矿物记录了从岩浆到热液的广泛形成条件，并揭示了岩石与热液流体或盐水在下大洋地壳环境中相互作用的复杂历史。在角闪石中Cl含量和阳离子配置的大的变化表明在可变的流体/岩石比与不同盐度的流体平衡形成。不同类型角闪石的87 Sr/86 Sr比值为0.7031 ~ 0.7039，δ 18 O稳定同位素组成为4.1 ‰ ~ 5.6‰，表明其形成环境为低流体/岩石比的岩石主导环境。然而，轻微偏离平均阿曼同位素值可能表明有海水在上述流体-岩石相互作用的影响。我们的研究提供了新的岩石学数据的辉长岩托管角闪石富脉在海水流体的存在下的亚固相线演化。
Hydrothermal veins and dykelets that cross-cut layered olivine gabbros deep in the plutonic section of the Samail Ophiolite, Sultanate of Oman, point towards the occurrence of hydrothermal circulation in the deep oceanic crust, and these features record interactions between rock and high temperature seawater-derived fluids or brines. Deep penetration of seawater-derived fluids down to 100 m above the Moho transition zone and the consequent interactions with the host rock lead to hydrothermal alteration from granulite facies grading down to greenschist facies conditions. Here we present a study of veins and dykelets formed by hydrothermal interaction cutting layered gabbro in the Wadi Wariyah, using petrographic, microanalytical, isotopic, and structural methods. We focus on amphiboles, which show a conspicuous compositional variation from high-Ti magnesiohastingsite and pargasite via magnesiohornblende and edenite, to Cl-rich ferropargasite and hastingsite (up to 1.5 a.p.f.u. Cl) and actinolite. These minerals record a wide range of formation conditions from magmatic to hydrothermal, and reveal a complex history of interactions between rock and hydrothermal fluid or brine in a lower oceanic crustal setting. Large variations in Cl content and cation configurations in amphibole suggest formation in equilibrium with fluids of different salinities at variable fluid/rock ratios. The presence of subsolidus amphibole extremely enriched in chlorine implies phase separation and brine/rock interactions.87Sr/86Sr values of 0.7031 to 0.7039 and stable δ18O isotopic compositions of 4.1 to 5.6‰ of the different amphibole types suggest a rock-dominated environment, i.e. with low fluid/rock ratios. However, the slight departure from mean Oman isotope values may indicate there was some influence of seawater in the aforementioned fluid-rock interactions. Our study provides new petrological data for the subsolidus evolution of gabbro-hosted amphibole-rich veins in the presence of a seawater-derived fluid.
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