Structure of the Lithosphere - Asthenosphere Boundary Across the Northeastern US Margin from Seafloor MT Data

从海底 MT 数据看美国东北部边缘的岩石圈-软流圈边界结构

• 批准号: 1536161
• 负责人: Robert Evans
• 金额: $ 17.4万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-08-15 至 2017-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1536161&HistoricalAwards=false
• 关键词: Structure; Lithosphere; Asthenosphere; Boundary; Across

The central mid-Atlantic region of the eastern North America margin is the focus of ongoing studies of rift processes. The region presents the opportunity to understand the role of pre-existing lithospheric weakness in guiding past continental rifting. The tectonic plate at this currently 'passive' margin thins through the transition from continental to oceanic crust, yet details of the topography on the base of the plate, as well as the properties of the underlying ductile mantle are not known. This information can provide clues about how Earth's tectonic plates evolve over time and why continents break up in the pattern that they do.Determination of the lithosphere-asthenosphere boundary (LAB) remains controversial, despite this boundary being one of the most fundamental aspects of the plate tectonics paradigm. In addition to limited knowledge about the topography on the base of the lithosphere, constraints on the properties of the uppermost asthenosphere immediately beneath the plate, are poor. Various interpretations have been presented to explain seismic observations across the margin, including a remnant thermal perturbation from a mantle plume, a hydrous upper mantle and the presence of partial melt. However, the thermal perturbation model is not consistent with a dramatically thinned lithosphere. This study will use magnetotelluric data to bring new constraints to the problem. Processing of data from 14 seafloor instruments deployed across the continental shelf offshore Martha's Vineyard, MA, and 2 stations on land will be accomplished. A 2-D resistivity model of the upper-mantle structure will be obtained and interpreted in terms of lithospheric alteration resulting from the influence of the Great Meteor hotspot. The depth to the LAB, the nature of the deeper continental lithosphere and whether melt is present at the top of the asthenosphere will be investigated.

北美洲东部边缘的大西洋中部地区是目前正在进行的裂谷过程研究的焦点。该区域提供了一个机会来理解先前存在的岩石圈弱点在引导过去的大陆裂谷中所起的作用。目前处于被动边缘的构造板块在从大陆地壳向洋壳过渡的过程中变薄，但板块底部的地形细节以及下伏韧性地幔的性质尚不清楚。这些信息可以提供有关地球构造板块如何随时间演化以及为什么大陆以这种方式分裂的线索。岩石圈-软流圈边界(LAB)的确定仍然存在争议，尽管这一边界是板块构造范例中最基本的方面之一。除了关于岩石圈底部地形的有限知识外，对紧邻板块下方的最上面软流层的性质的约束很差。已经提出了各种解释来解释边缘地区的地震观测，包括地幔热柱的残余热扰动、含水上地幔和部分熔融的存在。然而，热扰动模型与显著变薄的岩石圈并不一致。这项研究将利用大地电磁数据为这一问题带来新的约束。将完成对部署在马萨诸塞州玛莎葡萄园岛近海大陆架的14台海底仪器和陆地上2个测站的数据处理。将得到上地幔结构的二维电阻率模型，并根据大流星热点影响下的岩石圈变化进行解释。将对实验室的深度、大陆岩石圈更深的性质以及软流圈顶部是否存在熔体进行调查。