Collaborative Research: Completing North Pond Borehole Experiments to Elucidate the Hydrology of Young, Slow-Spread Crust

合作研究：完成北池钻孔实验以阐明年轻、缓慢扩张的地壳的水文学

• 批准号: 1634025
• 负责人: Charles Wheat
• 金额: $ 41.05万
• 依托单位: University of Alaska Fairbanks Campus
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-03-01 至 2018-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1634025&HistoricalAwards=false
• 关键词: Collaborative; Research; Completing; North; Pond

Seawater circulates through the upper part of the oceanic crust much like groundwater flows through continental aquifers. However, in the ocean this seawater circulation, many times heated by buried magmatic bodies, transports and releases 25% of the Earth's heat. The rate of fluid flow through ocean crust is estimated to be equal to the amount of water delivered by rivers to the ocean. Much of what we know of this subseafloor fluid flow comes from studies in the eastern Pacific Ocean on ocean crust created by medium and fast spreading mid-ocean ridges. These studies indicate that seawater and its circulation through the seafloor significantly impact crustal evolution and biogeochemical cycles in the ocean and affect the biosphere in ways that are just now beginning to be quantified and understood. To expand this understanding, this research focuses on fluid flow of seafloor generated by slow spreading ridges, like those in the Atlantic, Indian and Arctic Oceans because it is significantly different in structure, mineralogy, and morphology than that formed at fast and intermediate spreading ridges. This research returns to North Pond, a long-term; seafloor; fluid flow monitoring site, drilled and instumented by the Ocean Drilling Program in the Atlantic Ocean. This research site was punctured by boreholes in which fluid flow and geochemical and biological samplers have been deployed for a number of years to collect data and samples. It also provides resources for shipboard and on-shore geochemical and biological analysis. Broader impacts of the work include sensor and technology development, which increases infrastructure for science and has commercial applications. It also provides training for students and the integration of education and research at three US academic institutions, one of which is an EPSCoR state (Mississippi), and supports a PI whose gender is under-represented in sciences and engineering. Public outreach will be carried out in conjunction with the Center for Dark Energy Biosphere Investigations. This project completes a long-term biogeochemical and hydrologic study of ridge flank hydrothermal processes on slow-spreading, 8 million year old crust on the western flank of the Mid-Atlantic Ridge. The site, North Pond, is an isolated northeast-trending sediment pond, bounded by undersea mountains that have been studied since the 1970s. During Integrated Ocean Drilling Program Expedition 336 in 2011 and an expedition five months later (2012), sensors, samplers, and experiments were deployed in four borehole observatories drilled into the seafloor that penetrated into volcanic crust, with the purpose of monitoring changes in hydrologic properties, crustal fluid composition and mineral alteration, among other objectives. Wellhead sampling in 2012 and 2014 already revealed changes in crustal fluid compositions; and associated pressure data confirm that the boreholes are sealed and overpressured, reflecting a change in the formation as the boreholes recover from drilling disturbances. This research includes a 13-day oceanographic expedition and use of on-site robotically operated vehicles to recover downhole instrument packages at North Pond. It will allow the sampling of crustal fluids, recovering pressure data, and measuring fluid flow rates. Ship- and shore-based analyses will be used to address fundamental questions related to the hydrogeology of hydrothermal processes on slow-spread crust.

海水在洋壳上部循环，就像地下水流经大陆含水层一样。然而，在海洋中，这种海水循环多次被埋藏的岩浆体加热，输送和释放了地球25%的热量。据估计，流经洋壳的流体速率等于河流输送到海洋的水量。我们对海底流体流动的了解大部分来自于对东太平洋中、快速扩张的洋中脊所形成的洋壳的研究。这些研究表明，海水及其在海底的循环极大地影响了海洋中的地壳演化和生物地球化学循环，并以刚刚开始被量化和理解的方式影响着生物圈。为了扩展这种理解，本研究重点关注由慢速扩张脊产生的海底流体流，例如大西洋、印度洋和北冰洋的海底流体流，因为它在结构、矿物学和形态上与快速和中等扩张脊形成的流体显着不同。这项研究回到北塘，是一个长期的；海底；流体流动监测站点，由大西洋海洋钻探计划钻探并安装仪器。 该研究地点被钻孔刺穿，多年来一直在钻孔中部署流体流动以及地球化学和生物采样器来收集数据和样本。它还为船上和岸上地球化学和生物分析提供资源。 这项工作的更广泛影响包括传感器和技术开发，这增加了科学基础设施并具有商业应用。它还为三个美国学术机构（其中之一是 EPSCoR 州（密西西比州））的学生提供培训以及教育和研究的整合，并支持性别在科学和工程领域代表性不足的 PI。 公众宣传活动将与暗能量生物圈调查中心联合开展。 该项目完成了对大西洋中脊西翼缓慢扩张的 800 万年前地壳上的脊翼热液过程的长期生物地球化学和水文研究。该地点北池是一个孤立的东北走向的沉积池，周围是海底山脉，自 20 世纪 70 年代以来人们一直在研究这一点。在2011年的综合海洋钻探计划第336次远征和五个月后的一次远征（2012年）期间，传感器、采样器和实验被部署在钻入海底、深入火山壳的四个钻孔观测站中，目的是监测水文性质的变化、地壳流体成分和矿物蚀变等目标。 2012年和2014年的井口采样已经揭示了地壳流体成分的变化；相关压力数据证实钻孔被密封且超压，反映了钻孔从钻井干扰中恢复时地层的变化。这项研究包括为期 13 天的海洋学考察以及使用现场机器人操作车辆回收北池的井下仪器包。它将允许对地壳流体进行采样、恢复压力数据并测量流体流速。船基和岸基分析将用于解决与缓慢扩张的地壳热液过程的水文地质学相关的基本问题。