Accomplishment Based Renewal: An experimental study of phase separation and mineral fluid equilibria on iron and hydrogen transport in mid-ocean ridge hydrothermal systems

基于成就的更新：洋中脊热液系统中铁和氢传输的相分离和矿物流体平衡的实验研究

基本信息

批准号：
1736679
负责人：
William Seyfried
金额：
$ 43.1万
依托单位：
University of Minnesota-Twin Cities
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-08-15 至 2023-07-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1736679&HistoricalAwards=false
关键词：
Accomplishment Based Renewal experimental study

项目摘要

Hydrothermal circulation at mid-ocean ridges constitutes the largest geothermal system on Earth. Venting of spectacular plumes of hot, metal-bearing, fluid into seawater from sulfide structures on the seafloor along the volcanically active global mid-ocean ridge system is the end result of heat and chemical transfer between the ocean crust and the overlying ocean. As a result, the composition of seafloor hydrothermal vent fluids places a major control on ocean chemistry, as it has throughout Earth history. Seafloor hydrothermal fluids also provide dissolved gases and other chemicals to sustain microbial ecosystems that provide clues to the origin of life on Earth. The discovery of submarine hydrothermal venting and their accompanying microbial communities that do not require sunlight or organic matter created by photosynthesis to live, remains one of the most significant discoveries in modern science. The mechanisms, however, by which seawater is transformed to compositionally distinct hydrothermal vent fluids are uncertain, owing to the extreme temperatures and pressures of these processes. This research uses novel laboratory reactor and in-situ sensor systems to carry out first-of-a-kind experiments at the temperatures and pressures of seafloor hydrothermal venting to determine the effect of oxidation-reduction reactions and pH on mineral solubility at temperatures and pressure not previously studied. Goals of the work are to provide fundamental geochemical thermodynamic and kinetic parameters involving iron and hydrogen in water-rock interaction at high temperatures and pressures. The broader impacts of the work to research and science education include (1) Involvement of undergraduate science majors; (2) graduate student training in experimental and theoretical studies of mineral-fluid reaction which enhances their career opportunities; (3) development of new models to predict more accurately the links between the physical and chemical processes in natural multi-component hydrothermal systems; (4) physical infrastructure enhancement with the development of new equipment and techniques to conduct experiments and collect data in the area of phase separation of H2O; and, (5) public outreach in cooperation with K-12 programs at the Bell Museum of Natural History at the University of Minnesota. This research will acquire data to advance knowledge of mineral-fluid reactions that control the chemical evolution of mid-ocean ridge hydrothermal fluids. The experiments specifically address changes in dissolved Fe and H2 in fluids coexisting with mineral buffers at temperatures and pressures sufficient to cause phase separation in the NaCl-H2O system. The research will examine the possibility that fixing dissolved Fe and H2 in mineral-buffered reactions increases the solubility of these components in both fluid phases. This strategy contrasts sharply with previous fluid-only phase separation experiments where the inventory of dissolved Fe was limited. High Fe/Cl and Fe/Mn ratios and high dissolved H2 and H2S concentrations in vapor-rich vent fluids at mid-ocean ridges, especially in the aftermath of magmatic activity, implicate mineral buffering. Thus, the results of this experimental work will provide quantitative rigor to the presently qualitative observations of the temporal evolution of hydrothermal vent fluids at subseafloor temperatures approaching 500°C. These high temperature fluids have some of the highest dissolved Fe and H2 concentrations yet reported; but, in the absence of the experimental data, are difficult to interpret unambiguously in terms of subseafloor redox and pH controlling reactions. Scientific implications of the research will enable the development of theoretically-based predictive approaches for modeling aqueous speciation and mineral solubility in the low density and two-phase regions in the NaCl-H2O system. These conditions also apply to many continental hydrothermal systems. These terrestrial systems have immense scientific, economic, and practical significance and have critical importance to the Earth's thermal budget and geochemical cycles.

大洋中脊的热液循环构成了地球上最大的地热系统，沿着火山活跃的全球大洋中脊系统，将壮观的含金属热流体羽流从海底的硫化物结构排放到海水中。海洋地壳和上覆海洋之间的热量和化学传递因此，海底热液喷口流体的成分对海洋化学起着重要的控制作用，就像整个地球历史一样。海底热液还提供溶解的气体和其他化学物质来维持微生物生态系统，为地球上生命的起源提供线索，海底热液喷口及其伴随的微生物群落不需要阳光或光合作用产生的有机物就能生存。然而，由于这些过程的极端温度和压力，海水转化为成分不同的热液喷口流体的机制仍然是现代科学中最重要的发现之一。新型实验室反应器和原位传感器系统，在海底热液喷口的温度和压力下进行首次实验，以确定氧化还原反应和 pH 值对以前未研究过的温度和压力下矿物溶解度的影响这项工作的目标是提供涉及高温和高压下水-岩石相互作用中的铁和氢的基本地球化学热力学和动力学参数。这项工作对研究和科学教育的更广泛影响包括（1）本科生科学的参与。 (2) 矿物流体反应实验和理论研究方面的研究生培训，这增加了他们的职业机会；(3) 开发新模型以更准确地预测天然多组分热液系统中物理和化学过程之间的联系 (4) ）通过开发新设备和技术来增强物理基础设施，以在 H2O 相分离领域进行实验并收集数据；（5）与贝尔自然历史博物馆的 K-12 项目合作进行公共宣传；在明尼苏达大学。研究将获取数据，以增进对控制大洋中脊热液流体化学演化的矿物流体反应的了解。这些实验专门研究了在足以引起相分离的温度和压力下与矿物缓冲液共存的流体中溶解的铁和氢的变化。该研究将研究在矿物缓冲反应中固定溶解的 Fe 和 H2 是否会增加这些组分在两种流体相中的溶解度，这一策略与之前的纯流体相分离形成鲜明对比。在洋中脊富含蒸汽的喷口流体中，溶解的铁含量有限，特别是在岩浆活动之后，溶解的铁含量有限，而溶解的氢气和硫化氢浓度很高，这表明矿物缓冲作用。因此，这项实验工作的结果将为目前海底温度接近 500°C 时热液喷口流体的时间演化的定性观察提供定量的严谨性。这些高温流体具有一些最高温度。溶解的 Fe 和 H2 浓度尚未报告；但是，在缺乏实验数据的情况下，很难从海底氧化还原和 pH 控制反应方面明确解释该研究的科学意义，这将有助于开发基于理论的预测方法。 NaCl-H2O 系统中低密度和两相区域的水形态和矿物溶解度这些条件也适用于许多大陆热液系统，这些陆地系统具有巨大的科学、经济和实际意义。对地球的热收支和地球化学循环至关重要。