Collaborative Research: Pythia's Oasis - Access to Deep Subduction Zone Fluids

合作研究：皮提亚的绿洲 - 获取深俯冲带流体

• 批准号: 1658201
• 负责人: Deborah Kelley
• 金额: $ 39.03万
• 依托单位: University of Washington
• 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: 2017-09-15 至 2022-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1658201&HistoricalAwards=false
• 关键词: Collaborative; Research; Pythia; Oasis; Access

There is intense interest in understanding the nature, magnitude, and conditions of fluid flow deep within active continental margins due to the impact that fluids and mineral alteration processes have on seismicity and earthquakes in subduction zone environments. This is particularly true for the continental margin off Oregon and Washington State and Southern Canada, which is called the Cascadia Margin. This is because this ~1000 kilometer-long subduction zone fault has been locked since its last rupture in 1700 which produced a magnitude 9 earthquake that resulted in a large tsunami that impacted the Pacific Northwest and Japan and triggered significant underwater landslides. Gaining access to deep subduction zone fluids, however, is challenging because they are largely inaccessible, occurring at great depth below the seafloor. However, in 2015, a seep site was discovered off the Oregon coast where a jet of warm, hydrocarbon-enriched, low-salinity fluid was found venting from the seafloor. This site, called Pythia's Oasis, is unlike any seep site yet discovered, providing possible access, for the first time, to fluids formed deep within the Cascadia Subduction Zone. A second adjacent site includes an extensive collapse zone hosting multiple seeps that issue diffuse flows of warm and/or low salinity, methane-rich fluids that support dense microbial and macrofaunal communities. The goal of this two-year collaborative research project is to characterize the geology and chemistry of this extraordinary environment to test hypotheses about the origin of these fluids. This will be done using a remotely operated vehicle and an autonomous underwater vehicle from the National Deep Submergence Facility at the Woods Hole Oceanographic Institution, heat flow probes, coring devices, and geochemical tracers and analyses. If these fluids come from deep in the subduction zone, this site will provide an unprecedented opportunity to study high-temperature fluid sources and reactions in the only segment of the Cascadia Subduction Zone that is inferred to be seismically active. Results of the work have implications for understanding deep-seated fluid and seismogenic processes acting in other subduction zones as well. Broader impacts include an extensive at-sea student training program in which at least 10 undergraduate and graduate students will participate on the 13-day sea-going field expedition to the site where they will learn about and participate in seagoing activities and the discovery processes. The students will work alongside experienced scientists and ship and deep submergence vehicle crews to conducting their own research using data collected on the cruise and by later onshore analyses. Public outreach will be carried out via students who will communicate their experiences and findings through a cruise website and formal and informal presentations, with messaging focused on K-20 opportunities in integrated oceanography-engineering programs. This research will characterize the geology and chemistry of the extraordinary new discovery of a seep site, called Pythia's Oasis, that is located on the Cascadia Subduction Zone. Three hypotheses on the source of these fluids will be tested: (1) that the fluids are meteoric and play no role in the seismogenic behavior of the margin but may contribute to element transport between land and ocean, impacting the current understanding of coastal hydrogeology; (2) that the fluids originate from smectite-illite dehydration in the accreted sediments, rather than at the plate boundary, providing important information on fluid production and overpressure development within the accretionary prism above the plate boundary; and (3) that the fluids originate from high temperature metamorphic reactions at depth in the seismogenic region of the CSZ, resulting in extreme overpressures at the plate boundary. In the latter case, the dehydration reactions may explain the partially locked behavior of the fault in this part of the continental margin or suggest that the locked seismogenic zone may not correspond to moderate overpressures as postulated for other subduction zone areas such as Nankai. off Japan, and off Costa Rica. Hypotheses will be tested by detailed geological characterization of the seep site; by thoroughly analyzing the seep and pore fluids using major and trace element geochemistry; by examining the gas chemistry and by isotopic analyses; and by heat flow and modeling studies. The field program will utilize the remotely operated vehicle, Jason, and the autonomous underwater vehicle, Sentry, from the Woods Hole Oceanographic National Deep Submergence Facility to complete photomosaics of the seafloor as well as bathymetric maps around the seep sites at 1-m resolution. Seep fluids will be collected using isobaric gas-tight fluid-volatile samplers with real-time temperature measurements to determine end-member fluid compositions. All pore water samples will be analyzed for salinity, pH, and alkalinity shipboard, and a subset of samples will be analyzed for sulfate by shipboard ion chromatography. Approximately 300 samples will be analyzed for Cl, SO4, Br, Ca, Mg, Na, K, and alkalinity. Select samples will be analyzed for Li, Rb, Cs, Ba, DIC, and O/H isotopes. Si, NH4, as well as the methane through pentane concentrations in pore water and vent fluids will be analyzed. Stable isotope ratios of C, D, H, CH4, He, Li, and Cl will also be determined. Detailed heat flow measurements around the venting sites will be obtained to constrain relative changes in thermal gradients. Precisely located push cores for sediment chemical and physical property and pore water analyses will be collected and analyzed. Water column sensors on Sentry will also provide eH and CTD-O2-turbidity characterizations of the near-bottom fluids. Gravity coring will allow direct sampling of pore fluids below the zone of mixing with seawater and will ensure capture of the advecting fluid signal. Upward advection rates will be estimated from solute profiles using a new, non-steady-state, reaction-transport model. The spatial distribution of flow constructed from Jason push cores around the seep and shipboard gravity cores will be used to estimate output fluxes of fluid and solutes. The EM302 multibeam system on the R/V Thompson will be utilized for imaging of the bubble plumes to determine spatial extent with implications for biological activity in the upper water column. To determine local current regimes and hence the most intense plume locations in the water column, the hull-mounted 75 kHz ADCP will be used to log current velocities during all surveys.

由于流体和矿物质变化过程对俯冲带环境中的地震性和地震的影响，人们对了解流体流动的性质，大小和条件的浓厚兴趣。对于俄勒冈州，华盛顿州和加拿大南部的大陆边际尤其如此，这被称为卡斯卡迪亚利润率。这是因为自从1700年上一次破裂以来，这个约1000公里长的俯冲区断层已被锁定，这导致了9级地震，导致大型海啸影响了太平洋西北和日本，并引发了大量的水下滑坡。然而，获得深俯冲带流体的访问是具有挑战性的，因为它们在很大程度上无法访问，发生在海底以下的深度。然而，在2015年，在俄勒冈州海岸发现了一个渗水地点，那里发现了富含碳氢化合物的低含体，低含量的液体从海底排气。该地点称为毕田的绿洲，与尚未发现的任何渗水站点不同，这是首次可以进入卡斯卡迪亚俯冲带内形成的流体。第二个相邻的部位包括一个广泛的塌陷区，该区域容纳多种渗漏，它们发出了温暖和/或低盐度，富含甲烷的液体的弥漫流，这些流体富含甲烷的液体，这些液体支持密集的微生物和大型群落群落。这个为期两年的协作研究项目的目的是表征这种非凡环境的地质和化学，以检验有关这些流体起源的假设。这将使用远程操作的车辆和一辆自动驾驶的水下车辆从伍德斯孔海洋学机构，热流探针，加油装置以及地球化学示踪剂和分析的国家深层浸入式设施中进行。如果这些流体来自俯冲带的深处，则该部位将提供前所未有的机会，以研究Cascadia俯冲带的唯一部分中的高温流体来源和反应，这些降节带来了地震活性。这项工作的结果对理解作用在其他俯冲区域的深层液体和地震生成过程具有影响。更广泛的影响包括一项广泛的AT-SEA学生培训计划，其中至少有10名本科生和研究生将参加13天的海上野外探险，他们将学习并参与海上活动和发现过程。这些学生将与经验丰富的科学家，船舶和深层浸入式车辆人员一起工作，使用巡航和后来的陆上分析进行的数据进行自己的研究。公众推广将通过学生进行，他们将通过巡航网站以及正式和非正式演讲来传达他们的经验和发现，并关注综合海洋学工程计划的K-20机会。这项研究将表征位于卡斯卡迪亚俯冲带上的渗水景点的非凡新发现的地质和化学。将测试这些流体来源的三个假设：（1）流体是气象，在边缘的地震生成行为中没有作用，但可能有助于陆上和海洋之间的元素运输，从而影响当前对沿海水文学的理解； （2）流体起源于积聚沉积物中的蒙脱石 - 硅酸盐脱水，而不是在板边界上，提供了有关板界面上方的增生棱镜内的流体产生和过压发育的重要信息； （3）流体起源于CSZ的地震区域深度的高温变质反应，导致板边界处极端过压。 在后一种情况下，脱水反应可能解释了大陆边缘这一部分中断层的部分锁定行为，或表明锁定的地震生成区可能与其他俯冲区域（例如Nankai）所假定的中度过压可能不符。在日本和哥斯达黎加之外。假设将通过渗漏部位的详细地质表征来检验。通过使用主要和痕量元件地球化学彻底分析渗水和孔隙流体；通过检查气体化学和同位素分析；并通过热流和建模研究。现场计划将利用远程操作的车辆杰森（Jason）和自动驾驶的水下车辆，哨兵（Sentry），从伍兹孔海洋学国家全国深层浸入式设施中，以1-M分辨率以1-M分辨率完成海底的光摩萨以及seep地点周围的测深图。将使用带有实时温度测量的同型气密流体 - 挥发性采样器来收集渗流流体，以确定末端成员的流体组成。将分析所有孔隙水样品中的盐度，pH和碱度船上，并将通过船舶离子色谱法分析一部分样品的硫酸盐。将对CL，SO4，BR，CA，MG，NA，K和碱度分析大约300个样品。将对LI，RB，CS，BA，DIC和O/H同位素分析选定样品。将分析Si，NH4以及通过孔隙水和排气液中戊烷浓度的甲烷。 C，D，H，CH4，HE，LI和CL的稳定同位素比也将得到确定。将获得通风位点周围的详细热流量测量值，以限制热梯度的相对变化。将收集和分析精确的用于沉积物化学和物理特性的推动核心以及孔隙水分析。哨兵上的水柱传感器还将提供近底流体的EH和CTD-O2涡轮表征。重力芯将允许直接采样与海水混合区域下方的孔隙流体，并确保捕获前流的流体信号。使用新的非态，反应转移模型，将从溶质概况中估算向上的对流率。由Jason推动核心围绕渗流和船舶重力芯构建的流量的空间分布将用于估计流体和溶质的输出通量。 R/V Thompson上的EM302多光束系统将用于成像气泡羽流，以确定空间范围，对上水柱中的生物学活性的影响。为了确定局部当前状态，因此在水柱中最强烈的羽状位置，船体安装的75 kHz ADCP将在所有调查过程中用于记录电流速度。