Tracking Water‐Rock Interaction at the Atlantis Massif (MAR, 30°N) Using Sulfur Geochemistry
Tracking Water‐Rock Interaction at the Atlantis Massif (MAR, 30°N) Using Sulfur Geochemistry
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DOI：
10.1029/2018gc007813
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发表时间：
2018-11
期刊：
影响因子：
3.7
通讯作者：
J. Liebmann;E. Schwarzenbach;G. Früh-Green;C. Boschi;S. Rouméjon;H. Strauss;U. Wiechert;T. John
中科院分区：
文献类型：
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作者：
J. Liebmann;E. Schwarzenbach;G. Früh-Green;C. Boschi;S. Rouméjon;H. Strauss;U. Wiechert;T. John
海洋岩心杂岩体中超镁铁质岩石的热液蚀变和蛇纹岩化作用涉及流体与岩石之间广泛的元素交换和广泛的生物地球化学过程。由于海水硫酸盐的生物和非生物去除，这些过程影响了全球硫循环。因此，海底蛇纹石作用连接了水圈、生物圈和岩石圈。本文研究了位于大西洋中脊30°N的亚特兰蒂斯地块高蚀变基性和超基性样品的硫地球化学特征。分析的样本是在国际海洋探索计划第357次探险期间钻取的，并在2000年、2003年和2005年的阿尔文潜水期间收集。硫化物和硫酸盐相的多重硫同位素分析表明，在递进式热液蚀变过程中发生了几个过程：(1)海水硫酸盐的掺入；(2)高温（350-400°C）、低pH流体和浸出辉长岩侵入体产生的H2S的热化学硫酸盐还原；(3)微生物硫酸盐还原；(4)高水岩比下硫化物的氧化。岩石学检查表明，高T流体大多晚于蛇纹岩的形成，这些流体脉冲相对局部化（<1 dm尺度），导致矿物学高度不均匀。地球化学模拟表明，在微生物硫酸盐还原和氧化之后，局部发生了高T流体流入。总的来说，本研究记录了岩浆过程、流体-岩石相互作用和微生物活动的复杂相互作用，这些相互作用发生在海洋核复合体形成和地幔岩石暴露于海水中的地方。
Hydrothermal alteration and serpentinization of ultramafic rocks at oceanic core complexes involve extensive element exchange between fluid and rock and a wide range of biogeochemical processes. These processes influence the global sulfur cycle due to both biogenic and abiogenic removal of seawater sulfate. Hence, ocean floor serpentinization connects the hydrosphere, biosphere, and lithosphere. This work presents a study of the sulfur geochemistry of highly altered mafic and ultramafic samples from the Atlantis Massif located at 30°N along the Mid‐Atlantic Ridge. The analyzed samples were drilled during International Ocean Discovery Program Expedition 357 and collected during Alvin dives in 2000, 2003, and 2005. Multiple sulfur isotope analyses of sulfide and sulfate phases indicate that several processes took place during progressive hydrothermal alteration: (1) incorporation of seawater sulfate, (2) thermochemical sulfate reduction during interaction with high‐temperature (high‐T; 350–400 °C), low‐pH fluids and input of H2S derived from leaching gabbroic intrusions, (3) microbial sulfate reduction, and (4) oxidation of sulfides at high water‐rock ratios. Petrological examinations show that high‐T fluids mostly postdated the bulk serpentinization and that these fluid pulses were relatively localized (<1 dm scale) resulting in a highly heterogeneous mineralogy. Locally, high‐T fluid influx took place subsequent to microbial sulfate reduction and oxidation as indicated by geochemical modeling. Overall, this study documents the complex interplay of magmatic processes, fluid‐rock interaction, and microbial activity that take place during the formation of oceanic core complexes and where mantle rocks are exposed to seawater.