Collaborative Research: Seismic Structure and Evolution of Oceanic Crust along the Juan de Fuca Ridge and its Flanks

合作研究：胡安德富卡海岭及其侧翼的地震结构和洋壳演化

• 批准号: 0648303
• 负责人: Suzanne Carbotte
• 金额: $ 17.35万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-04-01 至 2011-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0648303&HistoricalAwards=false
• 关键词: Collaborative; Research; Seismic; Structure; Evolution

Hydrothermal circulation within the Earth's oceanic crust is a fundamental process that affects the chemical and physical exchange between the solid Earth and the oceans. Sea water penetrates down the ocean crust several kilometers through cracks, becomes heated up as it encounters magma reservoirs and hot rocks, reacts with the surrounding rocks, and rises back to the seafloor carrying minerals that are expelled into the oceans and used as nutrients by the vast biological communities that form deep-sea ecosystems. In addition, the interaction between the hydrothermal fluids and the rocks affects the chemical and physical properties of the lithosphere, therefore having important implications for processes like the formation of deep-sea mineral deposits. Within this general framework, this project will address the issue of what are the physical impact, depth extent, and horizontal spatial scales of hydrothermal alteration in the oceanic crust during its formation along a mid-ocean ridge, and its subsequent evolution and maturation.In particular, we want to understand (1) what is the relationship between high-temperature hydrothermal convection in a mid-ocean ridge and the underlying structure (location of magma reservoirs, porosity and permeability of the crust, etc.)? (2) How deep does the alteration penetrate as the crust matures? (3) Are there fine-scale variations in crustal structure related to topographic controls on low-temperature hydrothermal flow control? (4) What are the links between hydrothermal cooling and the observed variations in the structure of the oceanic crust near a mid-ocean ridge?Hydrothermal alteration has a significant impact on the speed at which seismic waves propagate through the crust (seismic velocity). Thus measuring in detail the seismic velocity of the upper ~1-2 km of the crust can give us a wealth of information about the processes described above. To answer the above-mentioned questions we will analyze marine seismic reflection data collected in 2002 as part of a NSF-funded project along the Juan de Fuca mid-ocean ridge and tectonic plate in the northeast Pacific, off the coast of Oregon, Washington, and British Columbia. Seismic waves generated from the research vessel M. Ewing were recorded by sensors located in a 6-km-long streamer towed by the ship. By measuring the time that waves traveled through the Earth's crust from the sources to the receivers, as well as their amplitude changes along their paths, we will be able to construct high resolution images of the elastic properties of the crust using state-of-the-art computing techniques known as travel-time and waveform seismic tomography. The resulting seismic tomography images will then be interpreted in terms alteration due to hydrothermal convection. We will also use gravity measurements to infer the density structure of the ocean crust, and together with the seismic observations, investigate the impact of hydrothermal cooling on the apparent variability of crustal thickness.Understanding the causes and consequences of hydrothermal circulation and alteration that takes place under the world's oceans requires a multidisciplinary approach, including biological, geochemical, geological, and geophysical studies, as well as numerical computer models and in-situ and remote observations. Much of what we know to date about hydrothermal circulation within oceanic lithosphere comes from studies at the Juan de Fuca ridge and tectonic plate during the past decades. This study will fill a gap by quantifying the impact and scales of hydrothermal alteration on the seismic structure of the lithosphere, and relate it to geological and environmental variables such as topography and sedimentation history.The objectives of this project are directly linked to the science goals of, and will benefit, several large initiatives and ongoing programs within Ocean Science. Our studies to characterize the structure beneath hydrothermal vent sites are directly linked to objectives of the NSF RIDGE-2000 program at the Endeavour ISS. CanNeptune and the Regional Cabled Observatory component of the Ocean Observatory Initiative will place a fiber optic cable spanning the Juan de Fuca plate to facilitate long-term monitoring of ridge axis and flank processes. The tomographic studies of axial structure of this project will provide new constraints on physical context at appropriate scales for these monitoring studies. Our ridge flank work will benefit plate-scale experiments envisioned here under ORION, and hydrogeologic objectives of ongoing ODP-IODP studies. This project will be part of the Ph.D. research of two graduate students, who will be trained in marine seismic reflection and tomography techniques. This will contribute to the development of a workforce with expertise in these methods, benefiting both the US academic research and industry communities.

地球海壳中的热液循环是一个基本过程，它会影响地球与海洋之间的化学和物理交换。海水通过裂缝穿透了几公里的海角，当岩浆储层和热岩石与周围的岩石反应时，它被加热，并升至载有矿物质的海底矿物质，并被驱散到海洋中，并被形成深海生态系统的庞大生物学社区用作营养。另外，水热流体与岩石之间的相互作用会影响岩石圈的化学和物理特性，因此对诸如形成深海矿物沉积物之类的过程具有重要意义。在这个一般框架内，该项目将解决沿海皮沿海层沿着海洋山脊形成过程中的水热改变的物理影响，深度和水平空间尺度的问题储层，孔隙率和地壳的渗透性等）？ （2）随着外壳的成熟，这种变化的深度有多深？ （3）与低温水热控制控制的地形控制相关的地壳结构中是否存在细尺度变化？ （4）水热冷却与海洋中山脊附近海洋壳结构的变化之间有什么联系？水热改变对地震波通过地壳传播（地震速度）的速度产生了重大影响。因此，详细测量地壳上部〜1-2 km的地震速度可以为我们提供有关上述过程的大量信息。为了回答上述问题，我们将分析2002年收集的海洋地震反射数据，这是NSF资助的项目的一部分，该项目沿Juan de Fuca Mid-ocean Ridge和东北太平洋，俄勒冈州，华盛顿州和不列颠哥伦比亚省的东北太平洋，东北太平洋地区的构造板和构造板。从研究船M.尤因产生的地震波是由位于船上拖曳6公里长的彩带中的传感器记录的。通过测量波浪从源到接收器的地壳中的波浪以及它们沿其路径的幅度变化的时间，我们将能够使用最先进的计算技术来构建外壳弹性特性的高分辨率图像。然后，将由于水热对流而用术语来解释所得的地震层析成像图像。我们还将使用重力测量来推断海角的密度结构，并与地震观测一起研究水热冷却对地壳厚度的明显变化的影响。理解水热循环的原因和后果以及在世界海洋中发生的，包括多种阶段的循环，包括多种阶段，包括地理学方法，地理学，地球，地球，地球循环，地球循环和变化。数值计算机模型以及原位和远程观察。迄今为止，关于海洋岩石圈中热液循环的大部分内容来自过去几十年来胡安·德福卡山脊和构造板的研究。这项研究将通过量化水热改变对岩石圈的地震结构的影响和尺度来填补空白，并将其与地质和环境变量（例如地形和沉积历史记录）相关联。该项目的目标与科学目标直接相关，并将受益于海洋科学中的一些大型计划和正在进行的计划。我们的研究表征了水热通风位置下的结构，直接与ISS努力ISS的NSF Ridge-2000计划的目标有关。海洋天文台倡议的罐装和区域电缆天文台组件将放置横跨胡安·德福卡板的光纤电缆，以促进对山脊轴和侧面工艺的长期监测。该项目轴向结构的层析成像研究将在适当尺度上为这些监测研究提供新的限制。我们的山脊侧面的工作将使在Orion下设想的板规规模实验以及正在进行的ODP-IODP研究的水文地质目标。该项目将是博士学位的一部分。对两名研究生的研究，他们将接受海洋地震反思和断层扫描技术的培训。这将有助于在这些方法方面具有专业知识的劳动力发展，从而使美国的学术研究和行业社区受益。