NSFGEO-NERC: Quantifying evolution of magmatism and serpentinisation during the onset of seafloor spreading

NSFGEO-NERC：量化海底扩张开始期间岩浆作用和蛇纹石化的演化

• 批准号: 2026866
• 负责人: Steven Constable
• 金额: $ 49.51万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-08-01 至 2024-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2026866&HistoricalAwards=false
• 关键词: NSFGEO; NERC; Quantifying; evolution; magmatism

This is a project that is jointly funded by the National Science Foundation’s Directorate of Geosciences (NSF/GEO) and the National Environment Research Council (NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award, each Agency funds the proportion of the budget and the investigators associated with its own ivestigators and component of the work.Ocean basins form when continents break up and rift apart, allowing mantle rock beneath to rise up between the continental margins, melt, and form new oceanic crust. When there is abundant melting, this process looks like the formation of oceanic crust at mid-ocean ridges. However, in some magma poor margins, the continental crust stretches and thins by faulting and allows mantle to rise beneath the crust and be exposed to water penetrating down faults. Combined with water, mantle forms a rock called serpentinite, rich in hydrated talc minerals and magnetite, a magnetic and electrically conductive mineral. It is important to understand more about the process of continental rifting but the seismic method, the most commonly used geophysical tool, has trouble differentiating between lower crustal rocks and serpentinized mantle. Electromagnetic (EM) geophysical methods allow the electrical conductivity of the crust and mantle to be imaged, and this project will use a combination of seismic methods and EM methods to study a magma poor margin southwest of the UK. From this a better understanding of the fundamental tectonic, chemical, and thermal history of continental breakup will be gained. The thermal history is important to the generation of hydrocarbons in this area.The breakup of continents involves a complex interplay of extensional tectonics and magmatism. The final stages of this process, resulting in the initiation of seafloor spreading, remain poorly understood. One common end-member involves hyper-extended continental crust and broad regions of exhumed and serpentinized (hydrated) mantle. Serpentinization at mid-ocean ridges, rifted margins and subduction zones mediates geochemical exchange between the lithosphere and the hydrosphere. There is evidence that normal faulting plays a key role in supplying fluids driving serpentinization beneath hyper-extended continental crust and possibly in regions of exhumed mantle. However, the seismic P-wave velocities of mafic crustal rocks and of serpentinized mantle rocks are similar, so interpretations of seismic data are uncertain. Serpentinized mantle rocks are generally more conductive, often by about an order of magnitude, than mafic crustal rocks, so controlled source electromagnetic (CSEM) and magnetotelluric (MT) techniques provide a promising route to resolve controversies around lithospheric structure. This project will focus on the magma-poor Goban Spur rifted margin to (i) acquire coincident high-quality CSEM, MT, and wide-angle seismic datasets along two carefully chosen transects; (ii) use these data to obtain coincident high-resolution seismic velocity and resistivity models for the upper few kilometers of the lithosphere, and lower-resolution models to tens of kilometers depth; (iii) interpret the resulting models to quantify regional and local variations in mantle serpentinization and magmatic addition; (iv) reconcile these observations with numerical models of lithospheric extension, mantle hydration, and decompression melting as seafloor spreading is initiated.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.

该项目由美国国家科学基金会地球科学理事会 (NSF/GEO) 和英国国家环境研究委员会 (NERC) 通过 NSF/GEO-NERC 牵头机构协议本协议共同资助。允许美国/英国联合提案提交，并由其研究人员拥有最大预算比例的机构进行同行评审。在成功联合确定资助后，每个机构将资助其预算比例和与其相关的研究人员。自己的调查员和当大陆分裂和裂开时，海洋盆地就形成了，使得下面的地幔岩石在大陆边缘之间升起，融化，并形成新的海洋地壳。当大量融化时，这个过程看起来就像海洋的形成。然而，在一些岩浆贫乏的边缘，大陆地壳因断层作用而拉伸和变薄，使得地幔上升到地壳下方，并暴露于渗透到断层中的水。地幔与水形成一种叫做蛇纹岩的岩石，富含水合滑石矿物和磁铁矿（一种磁性和导电矿物）。了解更多有关大陆裂谷过程的信息非常重要，但最常用的地球物理工具地震方法却存在困难。电磁（EM）地球物理方法可以区分下地壳岩石和蛇纹石化地幔，从而可以对地壳和地幔的电导率进行成像，该项目将使用结合地震方法和电磁方法来研究英国西南部的岩浆贫瘠边缘，可以更好地了解大陆破裂的基本构造、化学和热历史。热历史对于碳氢化合物的生成非常重要。大陆的分裂涉及伸展构造和岩浆作用的复杂相互作用，这一过程的最后阶段导致了海底扩张，但人们对其中一个常见的最终成员仍然知之甚少。超伸展的大陆地壳和大洋中脊、裂谷边缘和俯冲带的蛇纹石化（水合）地幔区域介导了岩石圈和水圈之间的地球化学交换。有证据表明，正常断层在其中起着关键作用。供应流体驱动超伸展大陆地壳下的蛇纹石化，并且可能在挖出的地幔区域中提供流体，然而，地震纵波。镁铁质地壳岩石和蛇纹石化地幔岩石的速度相似，因此地震数据的解释不确定，通常比镁铁质地壳岩石的导电性更强，通常高一个数量级，因此受控源电磁（CSEM）和大地电磁（MT）技术为解决围绕岩石圈结构的争议提供了一条有前途的途径，该项目将重点关注岩浆贫乏的戈班马刺裂谷边缘。 (i) 沿两条精心选择的横断面获取一致的高质量 CSEM、MT 和广角地震数据集；(ii) 使用这些数据获得岩石圈上部几公里的一致高分辨率地震速度和电阻率模型，以及数十公里深度的低分辨率模型；（iii）解释所得到的模型，以量化地幔蛇纹石化和岩浆添加的区域和局部变化；（iv）将这些观测结果与岩石圈的数值模型相一致；该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。