Collaborative Research: Testing the timing and direction of mantle exhumation at the Iberia-Newfoundland margins with low-temperature thermochronology

大陆向海底的转变是导致洋盆形成的重要构造过程。大陆解体导致大陆地壳极度减薄，在海底开始扩张之前，地幔岩石圈暴露在海底。研究最深入的是北大西洋的伊比利亚-纽芬兰边缘。以前关于伊比利亚-纽芬兰边缘的工作为我们理解这些盆地的结构提供了基础。然而，已经提出了多种模型，每种模型都略有不同。断层的时间、方向和数量直接影响这些边缘的演化，以及随后的海水变化，从而影响海底的宜居性。这项研究将解决导致大陆分离的断层作用的时间和结构问题。这项研究将使用磷灰石和锆石矿物来评估断层发生的时间和方向，以及边缘冷却到足以发生关键化学反应的时间。这些关键的反应被认为是理解地球上生命进化的关键。该项目将与南加州大学通信学博士生合作制作一部播客迷你系列片，探索该提案中的科学研究，并为不同的受众提供科学交流实践。此外，PIS实验室的一名研究生将为美国加州大学地球科学系和海洋与环境生物学系的研究生和本科生发起第一次多样性、公平性和包容性(DEI)海报会议。断层作用、岩浆作用和超长边缘的蛇纹岩作用之间的复杂相互作用推动了地球物理、地球化学和数值模拟研究数十年。然而，关于从大陆解体到地幔折返和海底扩张的时间和机制的一级问题，仍然存在争议。其中包括适合地幔折返的断层的时间关系，折返地幔剖面中断层的数量和方向性，以及地幔折返和海底改造过程中岩石圈的热历史。该项目是第一个全面的低温热年代学研究，旨在限制暴露在伊比利亚-纽芬兰边缘地幔段内及其附近的岩石的冷却历史，这是唯一进行了系统采样的超伸展边缘。该项目将使用从火成岩侵入体、同裂谷沉积物中回收的锆石和磷灰石，并从9个钻芯中挖掘出大陆地壳，这些岩芯构成了横跨挖掘出的地幔部分的水平横断面。这些数据将分别用于追踪蛇纹石化热窗口内~200℃(锆石(U-Th)/He)和~80℃(磷灰石(U-Th)/He)以下的岩石圈冷却。这些结果将被用来检验所提出的折返模型，并解决三个主要的研究问题：1)适应地幔折返的断裂作用与海底扩张之间的时间关系是什么？2)地幔折返是沿着一条主要的拆离线还是沿着多条断裂折返？3)地幔折返断裂的时间与其他构造和岩石学过程，包括海底扩张、蛇纹岩作用和岩浆作用的开始有什么关系？这些数据将被用来评估断裂、蛇纹岩和/或岩浆作用是发生在从东到西的渐进折返过程中，还是同时发生在几个地点，这对大陆解体向海底扩张的转变以及岩浆活动、岩石圈伸展和大洋中脊发展之间的关系具有关键意义。蛇纹岩化和黑云母形成的速度和程度也将对理解地球上适合生命的条件的发展产生影响。该项目将与南加州大学通信学博士生合作制作一部播客迷你系列片，探索该提案中的科学研究，并为不同的受众提供科学交流实践。此外，PIS实验室的一名研究生将为美国加州大学地球科学系和海洋与环境生物学系的研究生和本科生发起第一次多样性、公平和包容性(DEI)海报课程。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The change from continents to seafloor is an important tectonic process that leads to the formation of oceanic basins. Continental breakup results in extreme thinning of continental crust and exposure of mantle lithosphere to the seafloor before the start of seafloor spreading. The best-studied margin is the Iberia-Newfoundland margin in the North Atlantic. Previous work on the Iberia-Newfoundland margin provides the foundation for our understanding of the structure of these basins. However, multiple models have been proposed, each with slight differences. The timing, direction, and number of faults have direct implications on the evolution of these margins, as well as subsequent seawater alteration, which affects the habitability of the seafloor. This study will address questions on timing and structure of faulting that leads to separation of continents. This study will use the minerals apatite and zircon to evaluate the timing and direction of faulting, as well as when the margin cooled enough to allow key chemical reactions to occur. These key reactions are believed to be critical to understanding the evolution of life on Earth. The project will engage with a USC Communications PhD student to produce a podcast mini-series that explores the scientific research in this proposal and scientific communication practices for diverse audiences. In addition, a graduate student in the PIs lab will initiate the first Diversity, Equity, and Inclusion (DEI) poster session for graduate and undergraduate students from the Department of Earth Sciences and Department of Marine and Environmental Biology at USC.The complex interactions between faulting, magmatism, and serpentinization at hyper-extended margins have fueled geophysical, geochemical, and numerical modeling investigations for decades. However, there is still debate over first order questions about timing and mechanics of the transition from continental breakup to mantle exhumation and seafloor spreading. These include the temporal relationship of faults that accommodate mantle exhumation, the number and directionality of faults in the exhumed mantle section, and the thermal history of the lithosphere during mantle exhumation and seafloor alteration. This project is the first comprehensive low temperature thermochronology study to constrain the cooling history of the rocks exposed within and adjacent to the exhumed mantle section of the Iberia-Newfoundland margins, the only hyper-extended margin that has been systemically sampled. The project will use zircon and apatite recovered from igneous intrusions, syn-rift sediments, and exhumed continental crust from nine drill cores that make up a horizontal transect across the exhumed mantle section. These data will be used to track lithospheric cooling below ~200C (zircon (U-Th)/He) and ~80C (apatite (U-Th)/He), within the thermal window of serpentinization and ophicalcite formation, respectively. The results will be used to test proposed exhumation models and address three overarching research questions: 1) What is the temporal relationship between the faulting that accommodates mantle exhumation and seafloor spreading? 2) Was the mantle exhumed along one major detachment or multiple faults? 3) How does the timing of mantle exhumation faulting relate to other tectonic and petrologic processes, including the onset of seafloor spreading, serpentinization, and magmatism? These data will be used to evaluate whether faulting, serpentinization, and/or magmatism occurred over progressive exhumation from east to west or occurred in several locations simultaneously, with key implications for the transition from continental breakup to seafloor spreading and the relationship between magmatism, lithospheric extension, and mid-ocean ridge development. The rates and extents of serpentinization and ophicalcite formation will also have implications for understanding the development of conditions suitable for life on Earth. The project will engage with a USC Communications PhD student to produce a podcast mini-series that explores the scientific research in this proposal and scientific communication practices for diverse audiences. In addition, a graduate student in the PIs lab will initiate the first Diversity, Equity, and Inclusion (DEI) poster session for graduate and undergraduate students from the Department of Earth Sciences and Department of Marine and Environmental Biology at USC.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.