Collaborative Research: Quantifying Laurentia's Motion, Advancing Paleogeography and Constraining Rifting with New Paired Dates and Paleomagnetic Data from the Midcontinent Rift

在整个苏必利尔湖地区和美国中部大陆都有长期而大量的火山活动记录，这些火山活动在11亿年前几乎把北美分裂开来。由此产生的特征被称为中大陆裂谷。由于没能将北美分裂成独立的大陆，它保留了丰富的构造历史记录。这个项目将使用岩石的磁场测量和非常高精度的岩石同位素日期来确定11亿年前该地区构造板块的移动速度。主要研究人员将通过实地研究熔岩流，获得新的古地磁数据，并通过铀铅地质年代学制定高精度的岩石日期来实现这一目标。总的来说，这项研究解决了理解古代板块构造的本质和北美大陆构造演化的一个基本问题。除了项目的科学目标外，拟议的科学与加州四年级的科学标准相匹配，主要研究人员与奥克兰小学合作制定了一项扩展计划，包括课堂访问，最终在两个项目年份都对加州大学伯克利分校和劳伦斯科学馆进行实地考察。实践活动将为这些来自东奥克兰经济弱势社区的四年级学生带来项目科学的生活，并为来自代表性不足群体的学生提供机会，让他们设想自己参与STEM研究和地球科学的其他职业。该研究还支持研究生培训，支持早期职业研究人员，并为合作机构的研究基础设施做出贡献。研究结果将纳入研究课程，并将通过在会议和出版物上的发言广泛传播。从北美中大陆裂谷~1.1 Ga发育的表观极移路径（APWP）显示出古磁极位置的递进，与裂谷发育~ 2500万年的显著古地理变化相一致。这一进展意味着劳伦西亚板块运动的速度很快，但目前的速度估计有很大的不确定性，当极点位置和年龄的精度被强有力地综合起来时。此外，在目前的时间精度水平上，极位的快速变化导致了Laurentia与其他大陆之间允许的相对古地理位置的显著灵活性。我们建议从中大陆裂谷熔岩流中获得新的精确ID-TIMS 206Pb/238U日期，并将其与新开发的和现有的古地磁数据在地层背景下进行配对。“概念验证”数据表明，我们有能力利用U-Pb地质年代学的最新进展，获得与裂谷相关流动的现有日期相比，精度提高了近一个数量级的日期。通过对古地磁资料进行地层套接，获得新的精确年代，我们将有力地确定劳伦斯板块在20myr以上的运动速率，推进Rodinia组合时期的古地理重建，并进一步限制中大陆裂谷发育的速度。

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.