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

北美东部边缘的中大西洋中部地区是目前裂谷过程研究的重点。该地区提供了一个机会来了解先前存在的岩石圈弱点在指导过去大陆裂谷中的作用。目前，在这个“被动”边缘的构造板块在从大陆地壳到海洋地壳的过渡中变薄，但板块底部的地形细节以及下面的韧性地幔的性质尚不清楚。这些信息可以提供关于地球构造板块如何随时间演变的线索，以及为什么大陆会以这样的方式分裂。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式中最基本的方面之一。除了对岩石圈底部地形的了解有限之外，对板块下方最上层软流层性质的了解也很有限。人们提出了各种各样的解释来解释整个边缘的地震观测，包括地幔柱的残余热扰动、含水的上地幔和部分熔融的存在。然而，热扰动模型与岩石圈急剧变薄并不一致。本研究将利用大地电磁资料为这一问题带来新的约束。将完成对部署在玛莎葡萄园岛近海大陆架上的14台海底仪器和2个陆地观测站的数据处理。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蚀变进行解释。研究人员将研究陆缘的深度、较深大陆岩石圈的性质以及软流圈顶部是否存在熔体。

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.