Halogen Element and Stable Chlorine Isotope Fractionation Caused by Fluid-Rock Interaction (Bamble Sector, SE Norway)
Halogen Element and Stable Chlorine Isotope Fractionation Caused by Fluid-Rock Interaction (Bamble Sector, SE Norway)
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DOI：
10.1093/petrology/egv001
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发表时间：
2015-02-01
影响因子：
3.9
通讯作者：
Austrheim, Hakon O.
中科院分区：
文献类型：
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作者：
Kusebauch, Christof;John, Timm;Austrheim, Hakon O.
岩石和流体的广泛相互作用产生了区域尺度的岩石单元的蚀变和/或交代作用。挪威东南部班布尔地区的中上地壳岩石显示了复杂的变质和交代事件历史，并伴随着矿床的形成，这为研究区域尺度的流体-岩石相互作用提供了良好的背景。在这种热液环境中，卤素是岩石蚀变和矿金属运移的重要媒介。在这里，我们使用氟、氯、溴和碘的浓度和稳定的氯同位素比值(增量氯-37)来追踪两个辉长岩体的交代演化，并了解上地壳局部流体流动和普遍流体流动之间的相互作用。从原始辉长岩到角闪岩剪切带的蚀变序列显示出由普遍的流体侵入引起的递进角闪岩化和角闪岩化。卤素浓度和比率表明了单一流体的演化，导致在离剪切带最近的样品中富集氯、溴和碘。由于流体-矿物分配系数的差异，流体-矿物相互作用导致流体中卤素的富集性或贫乏，因为它与辉长岩发生广泛的反应。尽管方沸石的形成导致剪切带附近流体的逐步淡化，但辉长岩附近角闪石中氯浓度的增加反映了由于流体的干燥，向未改变的辉长岩方向的盐度增加。蚀变矿物的形成主要控制流体中卤素化学的变化，表明在流体-岩石相互作用过程中，卤素的行为并不完全保守。然而，演化的流体对仅在剪切带附近形成的蚀变矿物(如方沸石和黑云母)的稳定性具有反馈作用。蚀变程度最大的样品的BR/CI和I/CI比值分别为3×10(-3)和25×10(-6)，与海相孔隙流体测得的比值范围重叠。蒸发岩的再沸腾作用会产生明显较低的卤素比率，可以排除作为流体来源的可能性。未改变的辉长岩的C l-37值接近于0%，渗入流体也有类似的值。变化最小的样本，注意到存在
Pervasive interaction between rock and fluid produces regional-scale alteration and/or metasomatism of rock units. The middle and upper crustal rocks from the Bamble sector (SE Norway) show a complex history of metamorphic and metasomatic events, accompanied by ore deposit formation, which provides an excellent context for investigation of regional-scale fluid-rock interaction. Halogens are important agents of rock alteration and ore metal transportation in such hydrothermal regimes. Here we use F, Cl, Br and I concentrations and stable chlorine isotope ratios (delta Cl-37) to trace the metasomatic evolution of two gabbroic bodies and understand the interplay between localized and pervasive fluid flow in the upper crust. An alteration sequence was sampled from pristine gabbro to an amphibolitic shear zone, showing progressive amphibolitization and scapolitization caused by pervasive fluid ingress. Halogen concentrations and ratios suggest the evolution of a single fluid, causing enrichment of Cl, Br and I in samples nearest the shear zone. Owing to the differences in fluid-mineral distribution coefficients, fluid-mineral interaction resulted in either enrichment or depletion of halogens in the fluid as it reacted pervasively with the gabbro. Although scapolite formation leads to progressive desalination of the fluid near the shear zone, increasing Cl concentrations in amphibole near the gabbro reflect an increase in salinity towards the unaltered gabbro owing to desiccation of the fluid. The formation of alteration minerals mainly governs changes in the halogen chemistry of the fluid, showing that halogens do not behave fully conservatively during fluid-rock interaction. Nevertheless, the evolving fluid has a feedback on the stability of alteration minerals such as scapolite and biotite, which form only close to the shear zone. The Br/CI and I/CI ratios of the most highly altered samples are 3 x 10(-3) and 25 x 10(-6), respectively, and overlap with the range of ratios measured for marine pore fluids. Rennobilization of evaporites would have produced distinctly lower halogen ratios and can be ruled out as a fluid source. The unaltered gabbro has delta Cl-37 values near 0% and a similar value is inferred for the infiltrating fluid. Minimally altered samples, noted by the presence of