Fluid-rock interaction in ultramafic rocks considerably affects the chemical and isotopic composition of the oceanic lithosphere. We present a geochemical and petrological study of serpentinites and ophicalcites of the Northern Apennine ophiolite, Italy. This ophiolite sequence represents fragments of Jurassic oceanic lithosphere that have been denuded by low angle detachment faults, exposing peridotites on the ocean floor and triggering hydrothermal alteration. Seawater circulation is documented by (Jurassic) seawater-like ⁸⁷Sr/⁸⁶Sr values and δ¹³C values of 1.1–3.0‰ in carbonate veins of the ophicalcites. Bulk rock ophicalcites have low ⁸⁷Sr/⁸⁶Sr values of 0.70489–0.70599, elevated SiO₂ contents, and talc druses filling calcite veins that record Si-metasomatism. In contrast, underlying serpentinites have ⁸⁷Sr/⁸⁶Sr values above Jurassic seawater values. Bulk rock δD and δ¹⁸O values of ophicalcites and serpentinites suggest interaction with an evolved seawater-derived and/or magmatic fluid. These chemical signatures result from a complex history of serpentinization, carbonation, and metasomatism. Multiphase water-rock interaction includes infiltration of basement-derived fluids during initial mantle upwelling within an opening ocean basin, followed by localized high-temperature fluid infiltration, extensive seawater circulation resulting in carbonation, and oxidation near the seawater-exposed surface, and finally, fluid-rock interaction with overlying mafic lithologies leading to Si-metasomatism.

中文翻译：

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蛇纹石化，碳酸盐化和亚山绿岩蛇绿岩中超镁铁质层序的交代作用（意大利西北部）

超镁铁质岩石中的流体-岩石相互作用极大地影响了海洋岩石圈的化学和同位素组成。我们目前对意大利北部亚平宁蛇绿岩的蛇纹岩和蛇麻岩进行地球化学和岩石学研究。蛇绿岩序列代表侏罗纪海洋岩石圈的碎片，这些碎片被低角度分离断层剥蚀，使橄榄岩暴露在海床下并引发了热液蚀变。海水循环由（侏罗纪）海水状记录⁸⁷ SR / ⁸⁶的Sr的值和δ ^13个在ophicalcites的碳酸盐脉的1.1-3.0‰C值。散装岩液具有较低的⁸⁷ Sr / ⁸⁶ Sr值为0.70489–0.70599，SiO ₂较高内含物，滑石填满了方解石脉，记录了Si的致瘤作用。相反，下面的蛇纹岩具有高于侏罗纪海水值的⁸⁷ Sr / ⁸⁶ Sr值。全岩δD和δ ¹⁸ophicalcites和蛇纹岩的O值表明与演化的海水衍生和/或岩浆流体相互作用。这些化学特征来自蛇纹石化，碳酸化和交代的复杂历史。多相水-岩相互作用包括在开放的海盆内的初始地幔上涌过程中基底衍生的流体的渗透，随后局部高温流体的渗透，广泛的海水循环导致碳酸化以及暴露在海水暴露表面附近的氧化，最后，流体-岩石相互作用与上覆镁铁质岩性导致Si-超晶岩作用。