Heat and Fluid Flow at Pythia's Oasis, Cascadia Margin

卡斯卡迪亚边缘皮提亚绿洲的热量和流体流动

• 批准号: 1902446
• 负责人: Robert Harris
• 金额: $ 6.89万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-06-01 至 2022-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1902446&HistoricalAwards=false
• 关键词: Heat; Fluid; Flow; Pythia; Oasis

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 ~1000 kilometer-long subduction zone fault last ruptured 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. 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 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 research project is to better understand the heat flow around the sites in order to test hypotheses about the origin of these fluids and their effect on the environment. This will be done using a remotely operated vehicle from the National Deep Submergence Facility at the Woods Hole Oceanographic Institution and heat-flow probes from the Oregon State University, U.S. Academic Heat Flow Capability system. If these fluids come from deep in the subduction zone, this site will provide an 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 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 involve collecting heat flow data in and around Pythia's Oasis, a submarine seep on the convergent Cascadia margin, thereby providing a process-based understanding for the thermal and hydrologic regime of the shallow Cascadia subduction zone (CSZ). Pythia's Oasis is located ~80 km offshore Oregon and approximately 19 km landward of the deformation front. This seafloor seep has been discharging an enormous flux of warm (11.8 degree C), low salinity (-0.6 PSU), hydrocarbon bearing fluid over a multi-year time scale. Fluids being discharged there are hypothesized to result from high temperature ( 250 degree C) dehydration reactions that provide a view of deep-seated fluids. The principal goals of this experiment are to: 1) measure heat flow in the region of Pythia's Oasis, on the incoming plate, across the deformation front, and the accretionary prism, using a violin-bow style marine heat flow probe; 2) link these observations with previously collected values of heat flow (seafloor probe, BSR estimates and continental measurements), along strike and across the forearc; and 3) develop models to better understand the thermal regime of Pythia's Oasis and the Cascadia subduction zone. The proposed work will address fundamental and long-standing questions about the links between thermal, hydrologic and geodynamic processes and will advance discovery and understanding of this unique seep.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

由于流体和矿物蚀变过程对俯冲带环境中地震活动和地震的影响，人们对了解活动大陆边缘深处流体流动的性质、规模和条件有着浓厚的兴趣。对于俄勒冈州和华盛顿州以及加拿大南部的大陆边缘来说，情况尤其如此，这就是所谓的卡斯卡迪亚边缘。这条约1000公里长的俯冲带断层最后一次破裂是在1700年，当时发生了9级地震，导致了一场大海啸，影响了太平洋西北部和日本，并引发了重大的水下山体滑坡。然而，获得深俯冲带流体是一项挑战，因为它们基本上无法进入，发生在海底以下很深的地方。2015年，在俄勒冈州海岸发现了一个渗漏点，在那里发现了一股温暖、富含碳氢化合物、低盐度的流体从海底喷出。这个被称为皮提亚绿洲的地点不同于迄今为止发现的任何渗漏点，它提供了一个可能进入卡斯卡迪亚俯冲带深处形成的流体的通道。第二个相邻的网站包括一个广泛的塌陷区托管多个渗出问题的扩散流温暖和/或低盐度，富含甲烷的流体，支持密集的微生物和大型动物群落。该研究项目的目标是更好地了解这些地点周围的热流，以测试有关这些流体起源及其对环境影响的假设。这将使用伍兹霍尔海洋研究所国家深潜设施的遥控潜水器和俄勒冈州州立大学的热流探测器，美国学术热流能力系统。如果这些流体来自俯冲带深处，这个地点将提供一个机会，研究卡斯卡迪亚俯冲带中唯一被推断为地震活跃的部分的高温流体来源和反应。这项工作的结果对理解其他俯冲带中的深层流体和孕震过程也有影响。更广泛的影响包括一个海上学生培训方案，其中至少有10名本科生和研究生将参加为期13天的海上实地考察，他们将在那里了解和参与海上活动和发现过程。学生们将与经验丰富的科学家、船舶和深潜器船员一起工作，利用在巡航中收集的数据和后来的岸上分析进行自己的研究。公众宣传将通过学生进行，他们将通过游轮网站和正式和非正式的演讲交流他们的经验和发现，重点是K-20在综合海洋学工程项目中的机会。这项研究将涉及收集Pythia绿洲及其周围的热流数据，Pythia绿洲是收敛卡斯卡迪亚边缘的海底渗漏，从而为浅卡斯卡迪亚俯冲带（CSZ）的热量和水文状况提供基于过程的理解。 皮提亚绿洲位于俄勒冈州近海约80公里处，距离变形锋向陆地约19公里。 这种海底渗漏在多年的时间尺度内一直在排放大量温暖（11.8摄氏度）、低盐度（-0.6 PSU）的含烃流体。 据推测，那里排放的流体是由高温（250摄氏度）脱水反应造成的，这提供了深层流体的视图。 本实验的主要目的是：1）使用小提琴弓式海洋热流探针测量皮提亚绿洲地区的热流，在传入的板块上，穿过变形锋和增生棱镜; 2）将这些观测结果与先前收集的热流值联系起来（海底探测、BSR估算和大陆测量）、沿着走向和横跨前弧的研究; 3）开发模型以更好地了解皮提亚绿洲和卡斯卡迪亚俯冲带的热状况。 拟议的工作将解决有关热，水文和地球动力学过程之间的联系的基本和长期存在的问题，并将推进发现和理解这个独特的seep.This奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。