Throughout the Lake Superior region and the American midcontinent there is a record of prolonged and voluminous volcanic activity that nearly split North America apart 1.1 billion years ago. The resulting feature is known as the Midcontinent Rift. As a result of failing to break North America into separate continents, it preserves a rich record of tectonic history. This project will use magnetic measurements of rocks combined with very high precision isotopic dates on the rocks to determine how fast tectonic plates were moving in this region 1.1 billion years ago. The principal investigators will accomplish this by studying the lava flows in the field, obtaining new paleomagnetic data and developing high precision dates of rocks through uranium-lead geochronology. Overall, the research addresses a fundamental issue in understanding the nature of ancient plate tectonics and the tectonic evolution of the North American continent. In addition to the scientific goals of the project, the proposed science matches well with California fourth grade science standards and the principal investigators have partnered with an Oakland Elementary School to develop an outreach plan with classroom visits that culminate in a field trip to UC Berkeley and the Lawrence Hall of Science in both project years. Hands-on activities will bring project science to life for these fourth graders from an economically disadvantaged community in East Oakland and provide opportunities for students from underrepresented groups to envision themselves involved in STEM research and other careers in geosciences. The research is also supporting graduate student training, the support of an early career researcher, and is contributing to research infrastructure at the collaborative institutions. Results of the research will be incorporated into research curricula and will be widely disseminated through presentations at meetings and publications.
The apparent polar wander path (APWP) developed from the ~1.1 Ga North American Midcontinent Rift reveals a progression in paleomagnetic pole positions consistent with significant paleogeographic change during the ~25 million year history of rift development. This progression implies fast rates for Laurentia's plate motion, but current rate estimates have large uncertainty when the precision on pole locations and ages are robustly integrated. Additionally, the rapid change in pole position leads to significant flexibility in permissable relative paleogeographic positions between Laurentia and other continents at the current level of temporal precision. We propose to obtain new precise ID-TIMS 206Pb/238U dates from Midcontinent Rift lava flows that we will pair with newly developed and existing paleomagnetic data in stratigraphic context. "Proof of concept" data demonstrate our ability to leverage recent advances in U-Pb geochronology to obtain dates with nearly an order of magnitude improvement in precision in comparison to existing dates on rift-related flows. By stratigraphically bracketing paleomagnetic data with new precise dates, we will robustly determine the rates of Laurentia's plate motion over 20 Myr, advance paleogeographic reconstructions at this time period of Rodinia assembly and further constrain the tempo of Midcontinent Rift development.
