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

在苏必利尔湖地区和美国中大陆，有记录表明，11亿年前，持续时间长、规模巨大的火山活动几乎将北美分裂开来。由此形成的地貌被称为中大陆裂谷。由于未能将北美划分为不同的大陆，它保留了丰富的构造历史记录。该项目将使用岩石的磁性测量结合岩石上非常高精度的同位素测年来确定11亿年前该地区构造板块移动的速度。主要研究人员将通过研究野外的熔岩流动，获得新的古地磁数据，并通过铀-铅地质年代学开发高精度的岩石测年来实现这一点。总体而言，这项研究解决了一个基本问题，即了解古代板块构造的性质和北美大陆的构造演化。除了该项目的科学目标外，拟议的科学与加州四年级的科学标准非常匹配，主要研究人员与奥克兰一所小学合作，制定了一项外展计划，进行课堂访问，最终在两个项目年对加州大学伯克利分校和劳伦斯科学堂进行实地考察。实践活动将为这些来自东奥克兰经济困难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研究和其他地球科学职业。这项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。研究结果将被纳入研究课程，并将通过在会议和出版物上的陈述广泛传播。从~1.1Ga北美中大陆裂谷发展而来的视极游走路径(APWP)揭示了在约2500万年裂谷发展历史中，古地磁极点位置的进展与重大的古地理变化。这一进展意味着劳伦蒂亚板块运动的快速速率，但当极点位置和年龄的精确度被强有力地整合时，当前的速率估计有很大的不确定性。此外，极点位置的快速变化导致在目前的时间精度水平上，劳伦西亚和其他大陆之间允许的相对古地理位置具有很大的灵活性。我们建议从中大陆裂谷熔岩流中获得新的精确ID-TIMS 206Pb/238U年龄，我们将在地层学背景下与新开发和现有的古地磁数据配对。“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。通过用新的精确年代对古地磁数据进行地层划分，我们将有力地确定劳伦蒂亚板块在20Myr以上的运动速率，推进Rodinia集合期的古地理重建，并进一步制约中大陆裂谷的发育速度。

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.