Serpentinization, redox conditions, and metabolic energy production within shallow portions of subduction zones: windows to carbon cycling and chemosynthetic life driven by modern and ancient serpentinite mud volcanism

蛇纹岩泥火山是马里亚纳弧前海底令人印象深刻的海山，它排出来自俯冲太平洋板块的流体。这些流体含有丰富的蛇纹岩作用衍生的地质燃料(H2、CH4)，为泥火山内的化学合成生命提供了能量。有人认为蛇纹岩泥火山可能是地球上生命起源的潜在地点。但到目前为止，有多少维持生命的地球燃料是在弧前地幔中产生的，还没有得到量化。此外，由于地球燃料的可获得性，关键的生物地球化学过程是什么，这一点受到的限制很少。化石蛇纹岩泥火山中是否也发生了支持化学合成的生态系统的类似过程？我们建议进行一项全面的研究，以了解浅层(&lt；30公里)上俯冲带地幔中的氧化还原条件。我们将研究现代马里亚纳州泥火山的蛇纹岩，以及加利福尼亚州和俄勒冈州暴露的蛇纹岩泥火山化石。我们的联合经验模拟方法将产生O和S逸度的估计，由此可以计算相互作用流体的H2和H2S浓度。我们还将能够评估非生物有机合成的大范围反应的驱动力。马里亚纳州泥火山的来源深度是众所周知的。我们计划通过研究蛇纹岩中的变质碎屑在俯冲过程中经历的峰期变质条件来重建蛇纹岩化石矿床的源区深度。我们将进行岩石学和大量岩石/矿物化学工作，再加上计算的假截面，提供可靠的深度估计。我们进一步计划研究与蛇纹岩作用相关的代谢能量形成对化学合成生命和碳循环的影响。将研究保存在次生碳酸盐中的微生物活动的地球化学特征。样品包括马里亚纳泥火山的碳酸盐烟囱，以及蛇纹岩碎屑中的碳酸盐脉，以及与美国遗址的蛇纹岩矿床有关的富含化石的渗漏碳酸盐。脂类生物标志物和化合物特有的碳稳定同位素组成、矿物化学以及动力学和热力学模拟将有助于重建关键的生物地球化学过程和碳酸盐形成模式。拟议的工作旨在加深我们对俯冲带氧化还原条件及其对化学营养生命和大洋岩石圈深层碳循环的影响的理解。

Serpentinite mud volcanoes are impressive seamounts at the Mariana forearc seafloor that expel fluids derived from the subducted Pacific plate. These fluids contain abundant serpentinization-derived geofuels (H2, CH4), which provide energy for chemosynthetic life within the mud volcanoes. It has been suggested that serpentinite mud volcanoes are potential sites where life could have originated on Earth. But it has to date not been quantified how much of the life-sustaining geofuels are being produced in the forearc mantle. Moreover, it is poorly constrained what the key biogeochemical processes are that result from the availability of geofuels. And did similar processes supporting chemosynthesis-based ecosystems as well take place in fossil serpentinite mud volcanoes?We propose a comprehensive study to understand the redox conditions in the shallow (<30 km) supra-subduction zone mantle. We will investigate serpentinites from the modern Mariana mud volcanoes as well as from fossil serpentinite mud volcanoes exposed in California and Oregon. Our combined empirical–modeling approach will yield estimates of O and S fugacities, from which concentrations of H2 and H2S of the interacting fluids can be calculated. We will also be able to assess the driving force for a large range of reactions of abiogenic organosynthesis.The source depths of the Mariana mud volcanoes are well known. We plan to reconstruct the source depths of the fossil serpentinite deposits by examining the peak metamorphic conditions, which metamafic clasts included in the serpentinites experienced during subduction. We will conduct petrological and bulk rock-/mineral-chemical work that, coupled with calculated pseudosections, provides reliable depth estimates.We further plan to investigate the ramifications of the serpentinization-related formation of metabolic energy for chemosynthetic life and the carbon cycle. Geochemical signatures of microbial activity preserved within secondary carbonates will be studied. Samples comprise carbonate chimneys from the Mariana mud volcanoes as well as carbonate veins within serpentinite clasts and fossil-rich seep carbonates associated with the serpentinite deposits at the US sites. Lipid biomarkers and compound-specific carbon stable isotope compositions, mineral chemistry, as well as kinetic and thermodynamic modeling will allow reconstructing key biogeochemical processes and the modes of carbonate formation.The proposed work is designed to further our understanding of redox conditions in subduction zones and its consequences for chemotrophic life and the deep carbon cycle in the oceanic lithosphere.