气候变化领域集成服务门户(CCPortal): Reaction Mechanism and Water/Rock Ratios Involved in Epidosite Alteration of the Oceanic Crust

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DOI	10.1029/2020JB021540
	Reaction Mechanism and Water/Rock Ratios Involved in Epidosite Alteration of the Oceanic Crust
	Weber S.; Diamond L.W.; Alt-Epping P.; Brett-Adams A.C.
发表日期	2021
ISSN	21699313
卷号	126 期号:6
英文摘要	Epidosites are a prominent type of subseafloor hydrothermal alteration of basalts in ophiolites and greenstone belts, showing an end-member mineral assemblage of epidote + quartz + titanite + Fe-oxide. Epidosites are known to form within crustal-scale upflow zones and their fluids have been proposed as deep equivalents of black-smoker seafloor vent fluids. Proposals of the mass of fluid per mass of rock (W/R ratio) needed to form epidosites are contradictory, varying from 20 (Sr isotopes) to > 1,000 (Mg mobility). To test these proposals we have conducted a petrographic, geochemical and reactive-transport numerical simulation study of the chemical reaction that generates km3-size epidosite zones within the lavas and sheeted dike complex of the Samail ophiolite, Oman. At 250–400°C the modeled epidosite-forming fluid has pH ∼ 5.2, fO2 ≥ 10−20, low sulfur and extremely low Fe (10−6 mol/kg) contents. These features argue against a genetic link with black-smoker fluids. Chemical buffering by the epidosite fluid enriches the precursor spilites in Ca and depletes them in Na and Mg. Completion of the spilite-to-epidosite reaction requires enormous W/R ratios of 700–∼40,000, depending on initial Mg content and temperature. Collectively, the variably altered rocks in the Samail epidosite zones record flow of ∼1015 kg of fluid through each km3 of precursor spilite rock. This fluid imposed on the epidosite an Sr-isotope signature inherited from the previous rock-buffered chemical evolution of the fluid through the oceanic crust, thereby explaining the apparently contradictory low W/R ratios based on Sr isotopes. © 2021. The Authors.
英文关键词	epidosite; hydrothermal alteration; metasomatism; reactive-transport modeling; Samail ophiolite; water-rock ratio
语种	英语
来源期刊	Journal of Geophysical Research: Solid Earth
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/187067
作者单位	Institute of Geological Sciences, University of Bern, Bern, Switzerland
推荐引用方式 GB/T 7714	Weber S.,Diamond L.W.,Alt-Epping P.,et al. Reaction Mechanism and Water/Rock Ratios Involved in Epidosite Alteration of the Oceanic Crust[J],2021,126(6).
APA	Weber S.,Diamond L.W.,Alt-Epping P.,&Brett-Adams A.C..(2021).Reaction Mechanism and Water/Rock Ratios Involved in Epidosite Alteration of the Oceanic Crust.Journal of Geophysical Research: Solid Earth,126(6).
MLA	Weber S.,et al."Reaction Mechanism and Water/Rock Ratios Involved in Epidosite Alteration of the Oceanic Crust".Journal of Geophysical Research: Solid Earth 126.6(2021).