Establishing a Long-Term Geodetic Network at the East Pacific Rise Ridge 2000 Integrated Studies Site

在东太平洋海隆 2000 综合研究站点建立长期大地测量网络

• 批准号: 1342908
• 负责人: Scott Nooner
• 金额: $ 2.39万
• 依托单位: University of North Carolina at Wilmington
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-04-01 至 2014-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1342908&HistoricalAwards=false
• 关键词: Establishing; Long; Term; Geodetic; Network

Abstract Most of the world's plate boundaries are submerged beneath the oceans, and little is known about how these boundaries accommodate plate motion on monthly to yearly time scales. At mid-ocean ridges, new oceanic crust is formed as two oceanic plates move apart and magma is tapped from mantle upwelling beneath the ridge. Magma movement beneath active volcanoes on land has been tracked using a variety of geodetic techniques such as GPS and InSAR, however, to date there are few constraints on magma extraction beneath mid-ocean ridges. Lenses of melt (magma) have been identified both within the crust and at the crust mantle boundary, as well as a low seismic velocity mush (partial melt) zone beneath the crustal magma lens. Eruptions at the ridge crests presumably tap into these melt lenses but the fundamental scales associated with magma movement beneath ridge crests remain obscure. The questions to be addressed in this study include 1) What volume of the crustal melt lens is tapped by an eruption? How quickly does the melt lens get replenished from upwelling mantle? Does an eruption depend on horizontal transport of magma in a shallow dike? 2.) What is the rheologic structure of the ridge, including the width of the low viscosity mush zone? What is the mechanical behavior of the crust during and after an eruption? 3.) Do vents change temperature, chemistry flow rates, and location as the underlying magma lens evolves?We plan to address these questions by monitoring the vertical displacements of the seafloor at 9degrees50'N on the EPR in the vicinity of an eruption that occurred in early 2006. We will use a Mobile Pressure Recorder (MPR) in three campaign style surveys to measure the relative water pressure between different seafloor locations to determine changes in the relative elevation of benchmarks placed on the seafloor. Due to the buoyancy of the magma, surface deformation directly reflects the movement of magma below the surface. We expect to track the gradual movement of magma between eruption and diking events. We plan to compare processes under this fast-spreading ridge segment, which is underlain by a continuous, linear body of melt, to that of volcanoes elsewhere, which typically have a focused magma source. The temporal and spatial scales of recharging of the magma chamber post eruption will depend on the physical characteristics of the underlying mush zone and provide insight into the rheology of the surrounding crust. When paired with the co-located array Bottom Pressure Recorders (BPR) to be deployed in February 2007, both episodic and long-term deformation information will be available, tracking magma movements with hourly to yearly time scales. This will allow us, in collaboration with other researchers, to examine system relationships, such as the interplay between movements of magma, changes in hydrothermal vent systems, and microseismicity.Broader impacts This work will establish the infrastructure for long-term geodetic monitoring and begin accumulating a geodetic time series. All aspects of the ridge system are influenced or driven by the heat from magma that moves within the Earth's crust, which makes this work important in understanding all ridge systems and processes. Borrowing an instrument from Dr. Zumberge will promote collaboration between our two institutions. Public dissemination of the work will take place through peer reviewed publications and presentations at scientific conferences, interdisciplinary meetings, and seminars at other universities. We will work with the Ridge 2000 Education and Outreach office to educate the public about the significance of this project in understanding ridge systems, and how this work fits into the larger picture.

世界上大多数板块边界都淹没在海洋之下，人们对这些边界如何在月到年的时间尺度上适应板块运动知之甚少。在洋中脊，随着两个大洋板块分开，岩浆从洋中脊下的地幔上涌而出，新的洋壳形成。利用各种大地测量技术，如GPS和InSAR，可以跟踪陆地上活火山下的岩浆运动，然而，迄今为止，在大洋中脊下提取岩浆的限制很少。在地壳内部和壳幔边界均发现了熔融透镜，在地壳岩浆透镜下也发现了低地震速度的熔融（部分熔融）带。山脊顶部的喷发可能会进入这些熔融透镜，但与山脊下岩浆运动有关的基本规模仍然不清楚。在这项研究中需要解决的问题包括：1)地壳熔体透镜的体积有多大？熔融透镜从上涌的地幔中得到补充的速度有多快？喷发是否取决于浅岩脉中岩浆的水平移动？2.） 脊的流变结构是什么，包括低粘度糊状物区的宽度？地壳在喷发期间和之后的力学行为是什么？3.） 喷口是否会随着岩浆透镜体的演化而改变温度、化学流动速率和位置？我们计划在2006年初的一次喷发附近，通过监测EPR上北纬50度9度的海底垂直位移来解决这些问题。我们将在三个活动式调查中使用移动压力记录仪（MPR）来测量不同海底位置之间的相对水压，以确定放置在海底基准的相对高程的变化。由于岩浆的浮力，地表变形直接反映了地表下岩浆的运动。我们期望追踪岩浆在喷发和筑坝事件之间的逐渐运动。我们计划比较这个快速扩张的山脊段下的过程，它被一个连续的、线性的熔融体所覆盖，而其他地方的火山通常有一个集中的岩浆源。岩浆库在喷发后补给的时间和空间尺度将取决于下面的泥状带的物理特征，并提供对周围地壳流变学的深入了解。与将于2007年2月部署的位于同一位置的阵列底部压力记录仪（BPR）配合使用时，将可以获得短期和长期的变形信息，以每小时到每年的时间范围跟踪岩浆运动。这将使我们能够与其他研究人员合作，研究系统关系，例如岩浆运动、热液喷口系统变化和微地震活动之间的相互作用。这项工作将为长期大地测量监测建立基础设施，并开始积累大地测量时间序列。海脊系统的各个方面都受到地壳内部岩浆热量的影响或驱动，这使得这项工作对理解所有海脊系统和过程都很重要。借用Zumberge博士的仪器将促进我们两个机构之间的合作。这项工作将通过同行评议的出版物和在科学会议、跨学科会议和其他大学的研讨会上的报告向公众传播。我们将与Ridge 2000教育和推广办公室合作，教育公众了解这个项目在了解Ridge系统方面的重要性，以及这项工作如何融入更大的图景。