In-situ isotopic effects of serpentinization and identifying the controls on biological activity in serpentinites

蛇纹石化是超镁铁岩的热液蚀变作用，对全球许多地球化学循环有重要影响，是一种独特的矿物学过程，通过形成氢和甲烷支持生物活动。硫化物矿物中硫同位素特征形式的微生物活动证据已在沿大洋中脊沿着的许多橄榄岩热液系统和类似的古代系统（例如，大陆上的蛇绿岩序列）。最近的研究进一步表明，生物活性在蛇纹岩中长期储存硫和碳方面起着重要作用，对全球硫和碳循环具有潜在的深远影响。尽管如此，对橄榄岩所含热液系统中生物活动的控制，无论是在陆地上还是在海底，尚未得到最终证实，因此微生物活动对海底地球化学循环的影响仍然未知。这项研究将描述控制蛇纹岩中微生物活动的因素。将通过一种新的地球化学技术组合来评估蛇纹石化过程中生物活动与温度和流体化学之间的耦合，这种技术组合将表明这些关键参数如何随时间演变。 具体而言，将使用蛇纹岩中大量硫化物的多种硫同位素（32 S、33 S、34 S）分析和额外的、有针对性的、原位硫化物/硫酸盐同位素测量来检测微生物活性的存在。 这些数据将与详细的岩石学和矿物学检查以及寄主矿物相的原位同位素分析相结合。将研究三种不同构造环境和基本矿物学的蛇纹岩：（1）伊比利亚大陆边缘，（2）沿沿着大西洋中脊的15°20”N断裂带，（3）意大利亚平宁北方蛇绿岩序列中的蛇纹岩。 前两次钻探是作为综合大洋钻探计划（IODP）的一部分。 研究目标将是确定可变的流体成分和温度如何影响生物活动的发生。这些知识将为地球上生命的极限提供新的见解和限制，以及硫如何通过改变的海洋地壳循环，以及全球地球化学循环和不同地球水库之间的化学交换如何发生。该项目的更广泛影响涉及两名早期职业科学家的支持，他们都将接受使用新尖端技术的培训，促进弗吉尼亚理工大学和哈佛大学之间的合作，并让两名本科生参与科学。

Serpentinization, the hydrothermal alteration of ultramafic rocks, has an important impact on many global biogeochemical cycles and is a unique mineralogical process that can support biological activity through formation of hydrogen and methane. Evidence of microbial activity in the form of sulfur isotope signatures in sulfide minerals has been reported in many peridotite-hosted hydrothermal systems along mid-ocean ridges on the ocean floor and in analogous ancient systems (e.g., outcropping as ophiolite sequences on continents). Recent studies further suggest that biological activity plays a significant role in the long-term storage of sulfur and carbon within serpentinites with a potentially far-reaching impact on the global sulfur and carbon cycles. That said, controls on biological activity in peridotite-hosted hydrothermal systems, whether on land or under the sea, have not yet been conclusively proven and hence the impact of microbial activity on seafloor geochemical cycles remains unknown. This research will characterize the factors that control microbial activity within serpentinites. Determination of the coupling between biological activity and both temperature and fluid chemistry during serpentinization will be assessed via a novel combination of geochemical techniques that will indicate how these key parameters evolve through time. Specifically, multiple sulfur isotope (32S, 33S, 34S) analyses of bulk sulfides occurring in the serpentinites and additional, targeted, in-situ, sulfide/sulfate isotope measurements will be used to detect the presence of microbial activity. These data will be combined with detailed petrological and mineralogical examination and in-situ isotope analyses of host mineral phases. Serpentinites from three different tectonic settings and basic mineralogies will be examined: (1) the continental Iberian Margin, (2) the 15°20" N fracture zone along the Mid-Atlantic Ridge, and (3) serpentinites from an ophiolite sequence in the Northern Apennine, Italy. the first two were drilled as part of the Integrated Ocean Drilling Program (IODP). Research goals will be to determinee how variable fluid compositions and temperatures affect the occurrence of biological activity. This knowledge will provide new insights and constraints on the limits of life on Earth and how sulfur is cycled through altered oceanic crust, as well as how global geochemical cycles and the chemical exchange occur between different Earth reservoirs. Broader impacts of the project involve the support of two early career scientists, both of whom will be trained in the use of new cutting-edge techniques, foster collaboration between Virginia Tech and Harvard University, and engage two undergraduate students in the science.