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

从大陆到海底的变化是导致海洋盆地形成的一个重要构造过程。在海底扩张开始之前，大陆分裂导致大陆地壳极度变薄，地幔岩石圈暴露在海底。研究得最好的是北大西洋的伊比利亚-纽芬兰边缘。以前对伊比利亚-纽芬兰边缘的研究为我们理解这些盆地的结构提供了基础。然而，已经提出了多个模型，每个模型都略有不同。断裂的时间、方向和数量直接影响这些边缘的演化，以及随后的海水蚀变，从而影响海底的可居住性。这项研究将解决导致大陆分离的断层的时间和结构问题。这项研究将使用矿物磷灰石和锆石来评估断层的时间和方向，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传播学博士生合作，制作一个播客迷你系列，探索本提案中的科学研究和面向不同受众的科学传播实践。此外，PIs实验室的一名研究生将为南加州大学地球科学系和海洋与环境生物系的研究生和本科生发起第一次多样性、公平和包容（DEI）海报会议。几十年来，断层作用、岩浆作用和超延伸边缘蛇纹岩化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。然而，关于从大陆分裂到地幔挖掘和海底扩张过渡的时间和机制的一级问题仍然存在争议。其中包括地幔挖掘断层的时间关系、地幔挖掘剖面断层的数量和方向，以及地幔挖掘和海底蚀变过程中岩石圈的热史。该项目是第一个全面的低温热年代学研究，旨在限制伊比利亚-纽芬兰边缘的地幔部分及其附近暴露的岩石的冷却历史，这是唯一一个系统采样的超延伸边缘。该项目将使用从火成岩侵入物、同裂谷沉积物和从9个钻孔岩心中挖掘出的大陆地壳中回收的锆石和磷灰石，这些岩心构成了挖掘出的地幔剖面的水平样带。这些数据将分别用于在蛇纹岩化和蛇方石形成的热窗内追踪~200C（锆石(U-Th)/He）和~80C（磷灰石(U-Th)/He）以下的岩石圈降温。研究结果将用于检验提出的挖掘模型，并解决三个主要的研究问题：1)地幔挖掘与海底扩张的断层之间的时间关系是什么？2)地幔是沿着一个主要拆离发掘的，还是沿着多个断裂发掘的？3)地幔掘出断裂的时间与其他构造和岩石学过程（包括海底扩张、蛇纹岩化和岩浆作用的开始）的关系如何？这些数据将用于评估断裂、蛇纹岩化和/或岩浆作用是否发生在从东到西的渐进挖掘过程中，或同时发生在几个地点，对大陆分裂到海底扩张的过渡以及岩浆作用、岩石圈延伸和洋中脊发育之间的关系具有重要意义。蛇纹石化和蛇方石形成的速度和程度也将对了解地球上适合生命生存的条件的发展产生影响。该项目将与南加州大学传播学博士生合作，制作一个播客迷你系列，探索本提案中的科学研究和面向不同受众的科学传播实践。此外，PIs实验室的一名研究生将为南加州大学地球科学系和海洋与环境生物系的研究生和本科生发起第一次多样性、公平和包容（DEI）海报会议。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.