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

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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.