Collaborative Research: Quantifying the thermal effects of fluid circulation in oceanic crust entering the Cascadia subduction zone

合作研究：量化进入卡斯卡迪亚俯冲带的洋壳中流体循环的热效应

• 批准号: 2034872
• 负责人: Robert Harris
• 金额: $ 19.33万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-06-01 至 2025-05-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2034872&HistoricalAwards=false
• 关键词: Collaborative; Research; Quantifying; thermal; effects

Collaborative Research: Quantifying the thermal effects of fluid circulation in oceanic crust entering the Cascadia subduction zoneSubduction zones, where one tectonic plate moves under another, generate the world’s largest earthquakes and tsunamis. Temperatures along the subduction zone fault that separates the two tectonic plates affect friction, thus influencing the size and distribution of earthquakes. In addition, subduction zone temperatures affect a wide range of other physical and chemical processes, including the generation of magma that supplies some volcanoes. To understand these processes, it is important to accurately estimate subduction zone temperatures. Seawater circulating in the subducting tectonic plate can be an important control on subduction zone temperatures. For the Cascadia subduction zone offshore the Pacific Northwest of the United States, the spatial extent and vigor of this seawater circulation is not well known, leading to substantial uncertainty in temperature estimates for this hazardous subduction zone. This study will collect temperature measurements in seafloor sediments offshore Washington and Oregon, and map the distribution of those sediments, to understand the controls on temperatures in the system and improve estimates of subduction zone temperatures. The results of this research have direct societal benefit, by informing earthquake hazard estimates. In addition, the proposed project will enhance education at New Mexico Tech, a STEM-focused Hispanic-serving institution. Two graduate students will be trained in geophysics and hydrogeology. Results of the project will be incorporated into “using data in the classroom” efforts, improving hands-on experience in undergraduate courses.Accurate estimates of subduction zone temperatures are required to understand a variety of critical processes, including controls on seismogenic and aseismic behavior on subduction megathrusts. For the Cascadia subduction zone, the dearth of instrumentally recorded interplate seismicity requires a reliance on indirect methods (including temperature) to estimate the extent of the seismogenic zone. The extent to which fluid circulation redistributes heat within the subducting plate has profound implications for temperature distributions in the Cascadia subduction zone. In Cascadia, a lack of heat flux data immediately seaward of the deformation front is a significant knowledge gap for understanding subduction zone temperatures. This study will fill this hole by collecting ~600 km of seismic reflection lines and ~200 heat flux measurements at 5 sites offshore Washington and Oregon with a focus on quantifying the extent and vigor of hydrothermal circulation in the Juan de Fuca plate. Hydrothermal circulation associated with basement relief generates large anomalies in heat flux across the seafloor; this signal provides a test for the presence of hydrothermal circulation. Combining data from multiple sites will provide information on whether hydrothermal circulation is local or regional. The central hypotheses are: 1) Hydrothermal circulation is ubiquitous in the upper oceanic crustal aquifer; it persists in the aquifer covered by a thick mantle of sediment near the deformation front and in the shallowly subducted crust; and 2) Pseudofaults along propagator wakes are zones of high permeability through the full thickness of the crust; thus, they are zones of enhanced fluid and heat circulation relative to areas outside of propagator wakes. Comparisons of mean heat flux values with those predicted from lithospheric cooling models will allow assessment of whether heat in addition to the basal heat flux is added to the system (e.g., heat transported seaward through the subducting oceanic crust and/or heat advected upwards through faults in propagator wakes). Analyzing and interpreting the controls on the thermal state of the Juan de Fuca plate near the deformation front will allow for the development of improved predictive models of subduction zone temperatures.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.

合作研究：量化进入卡斯卡迪亚俯冲带的海洋地壳流体循环的热效应俯冲带，一个构造板块在另一个构造板块下移动，产生世界上最大的地震和海啸。分隔两个构造板块的俯冲带断层沿线的温度影响摩擦，从而影响地震的大小和分布。此外，俯冲带的温度还影响着其他广泛的物理和化学过程，包括为一些火山提供岩浆的产生。为了了解这些过程，准确估计俯冲带的温度是很重要的。俯冲构造板块内的海水循环是控制俯冲带温度的重要因素。对于美国西北太平洋沿岸的卡斯卡迪亚俯冲带，这种海水环流的空间范围和活力尚不清楚，导致对这一危险俯冲带的温度估计存在很大的不确定性。这项研究将收集华盛顿州和俄勒冈州近海海底沉积物的温度测量数据，并绘制这些沉积物的分布图，以了解系统中对温度的控制，并改进对俯冲带温度的估计。这项研究的结果具有直接的社会效益，为地震危害评估提供了信息。此外，拟议中的项目将加强新墨西哥理工大学（New Mexico Tech）的教育，这是一所专注于stem的西班牙裔服务机构。两名研究生将接受地球物理和水文地质学方面的培训。该项目的成果将纳入“在课堂上使用数据”的努力，提高本科课程的实践经验。对俯冲带温度的准确估计是了解各种关键过程的必要条件，包括对孕震的控制和对俯冲特大逆冲的地震行为。对于卡斯卡迪亚俯冲带，由于缺乏仪器记录的板块间地震活动，需要依靠间接方法（包括温度）来估计发震带的范围。流体循环在俯冲板块内重新分配热量的程度对卡斯卡迪亚俯冲带的温度分布具有深远的影响。在卡斯卡迪亚，缺乏变形锋直接向海方向的热通量数据是理解俯冲带温度的一个重要知识缺口。本研究将通过在华盛顿和俄勒冈州近海的5个地点收集约600公里的地震反射线和约200个热通量测量值来填补这一空白，重点是量化Juan de Fuca板块热液循环的程度和活力。与基底起伏相关的热液环流在整个海底产生了较大的热通量异常；这一信号为热液环流的存在提供了一种检验。综合多个地点的数据将提供关于热液循环是局部的还是区域性的信息。主要假设为：1)热液环流在大洋上部地壳含水层普遍存在；它存在于变形前缘附近被厚地幔覆盖的含水层和浅俯冲地壳中；2)沿传播尾迹的假断层是贯穿整个地壳的高渗透率带；因此，相对于传播尾迹以外的区域，它们是流体和热循环增强的区域。将平均热通量值与岩石圈冷却模式预测的值进行比较，可以评估除基底热通量外，是否有热量加入系统（例如，热量通过俯冲的海洋地壳向海输送，和/或热量通过传播体尾迹中的断层向上平流）。分析和解释变形锋附近Juan de Fuca板块热状态的控制因素，将有助于发展改进的俯冲带温度预测模型。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Thermally Significant Fluid Seepage Through Thick Sediment on the Juan de Fuca Plate Entering the Cascadia Subduction Zone

进入卡斯卡迪亚俯冲带的胡安德富卡板块上厚沉积物的热显着流体渗漏

• DOI: 10.1029/2023gc010868
• 发表时间: 2023
• 期刊: Geosystems
• 作者: Norvell, Benjamin;Kyritz, Thomas;Spinelli, Glenn A.;Harris, Robert N.;Dickerson, Kristin;Tréhu, Anne M.;Carbotte, Suzanne;Han, Shuoshuo;Boston, Brian;Lee, Michelle
• 通讯作者: Lee, Michelle