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

由于流体和矿物蚀变过程对俯冲带环境中的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、规模和条件非常感兴趣。俄勒冈州、华盛顿州和加拿大南部的大陆边缘尤其如此，被称为卡斯卡迪亚边缘。这条约1000公里长的俯冲带断层上一次破裂是在1700年，当时发生了9级地震，引发了一场大海啸，冲击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，获取深俯冲带流体是具有挑战性的，因为它们基本上是无法获取的，发生在海底以下的很深的地方。2015年，在俄勒冈州海岸附近发现了一个渗漏点，在那里发现了一股温暖的、富含碳氢化合物、低盐度的流体从海底喷涌而出。这个地点被称为皮提亚绿洲，与目前发现的任何渗漏地点不同，它提供了进入卡斯卡迪亚俯冲带深处形成的流体的可能途径。毗邻的第二个地点包括一个广泛的塌陷带，其中有多个渗漏，这些渗漏导致温暖和/或低盐度、富甲烷的流体扩散流动，支持密集的微生物和大型动物群落。这项研究项目的目标是更好地了解现场周围的热流，以便检验关于这些流体的来源及其对环境影响的假说。这将使用伍兹霍尔海洋研究所国家深潜设施的远程操作工具和俄勒冈州立大学美国学术热流能力系统的热流探测器来完成。如果这些流体来自俯冲带深处，这个地点将提供一个机会来研究卡斯卡迪亚俯冲带唯一被推测为地震活动的段的高温流体来源和反应。这项工作的结果对理解深部流体和作用于其他俯冲带的地震孕育过程也有意义。更广泛的影响包括一个海上学生培训计划，在该计划中，至少10名本科生和研究生将参加为期13天的海上实地考察，在那里他们将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以及船舶和深潜潜水器工作人员合作，利用邮轮上收集的数据和后来的岸上分析进行自己的研究。将通过学生进行公众宣传，他们将通过邮轮网站和正式和非正式的演示交流他们的经验和发现，重点是K-20海洋工程综合项目的机会。这项研究将涉及收集皮提亚绿洲及其周围的热流数据，这是一个位于会聚的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)的热和水文状况提供基于过程的了解。皮提亚的绿洲位于俄勒冈州近海约80公里处，距离变形前缘约19公里。在多年的时间尺度上，这个海底渗漏一直在释放大量温暖(11.8摄氏度)、低盐度(-0.6PSU)的含烃流体。在那里排出的流体被认为是高温(250摄氏度)脱水反应的结果，这些反应提供了深层流体的景象。这项实验的主要目标是：1)使用小提琴弓形海洋热流探测器测量皮提亚绿洲区域、来袭板块上、穿过变形锋面和吸积棱镜的热流；2)将这些观测结果与以前收集的沿走向和跨弧的热流值(海底探测器、BSR估计和大陆测量)联系起来；3)建立模型，以更好地了解皮西亚绿洲和卡斯卡迪亚俯冲带的热状况。这项拟议的工作将解决关于热、水文和地球动力学过程之间联系的根本和长期存在的问题，并将促进对这一独特渗漏的发现和理解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.