Collaborative Research: Paleomagnetism and Geochronology of Mafic Dikes in Morocco, Reconstructing West Africa in Proterozoic Supercontinents

合作研究：摩洛哥镁铁质岩脉的古地磁学和地质年代学，重建元古代超大陆中的西非

• 批准号: 1953549
• 负责人: David Evans
• 金额: $ 39.04万
• 依托单位: Yale University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-07-01 至 2024-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1953549&HistoricalAwards=false
• 关键词: Collaborative; Research; Paleomagnetism; Geochronology; Mafic

Over billions of years of Earth history, continents have drifted across the globe, periodically assembling into supercontinents. Pangea was the most recent of these: a single landmass that joined the Americas to Europe and Africa, prior to spreading of the Atlantic Ocean. Pangea was likely preceded by more ancient supercontinents named Rodinia (about 900 million years ago) and Nuna (about 1.5 billion years ago), both existing within the “Proterozoic” time interval of primordial life. Although these supercontinents have names, their exact arrangements of continental fragments remain uncertain. Regardless, geologists are beginning to speculate on whether the supercontinental transitions generally have an accordion-like pattern of motion (imagine a future for the Americas reversing their course and drifting eastward to close the Atlantic Ocean and re-collide with Europe and Africa), or whether continents circumnavigate the globe (imagine the Americas continuing to drift westward to close the Pacific Ocean and collide with eastern Asia and Australia, thus turning the old supercontinent “inside-out”). These ideas help shape our view of Earth’s evolving deep interior over billions of years, and also give geographical context to the formation of mineral deposits, ancient climate records, and biological evolution at the longest timescales. This project uses two complementary methods of laboratory measurement to determine how the continents have moved across the Earth’s surface: paleomagnetism—the ancient record of the geomagnetic field that is recorded by rocks; and the isotopic dating of the age of rocks using the radioactive decay of uranium to lead. The project focuses on the least well-understood continental fragment in the Nuna and Rodinia supercontinental landmasses: the West African craton. Within West Africa, particularly the Anti-Atlas Mountains of Morocco, recent advances of geological understanding provide an opportunity to apply the two methods to ancient volcanic rock systems (“mafic dikes”) of a variety of ages, to produce more accurate reconstructions of the Nuna and Rodinia landmasses and to discover the patterns of Earth’s supercontinental transitions. The project will involve collection of rock samples in the field, laboratory analyses on those specimens, and publication of results in peer-reviewed journals. In addition to the scientific goals of the project, important societal outcomes associated with this project include training the next generation of Earth scientists in an important science, technology, engineering and mathematics (STEM) discipline; incorporation of the project’s results into public museum displays; and development of educational modules with K-12 public school teachers.Uncertainties in the configurations of supercontinents Nuna and Rodinia currently permit either of two end-member views on long-term global geodynamics: whether supercontinents tend to revert to prior configurations, or turn “inside-out.” It is also possible that they have alternated between those two patterns in time. West Africa's paleogeography is the least constrained of all major Precambrian cratons, and its previously hypothesized placement either within the middle of pre-Pangean supercontinents or along their periphery is crucial to the aforementioned debate. This project seeks to conduct an integrated paleomagnetic and geochronological study of mafic dike swarms in Precambrian inliers of the Anti-Atlas Mountains, Morocco. High-quality and precisely dated paleomagnetic poles obtained from this study will fill a notable gap in the tectonic and kinematic history of West Africa and neighboring blocks in Nuna and Rodinia, and provide essential ground-truth to the debate on supercontinental transitional styles.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.

在地球数十亿年的历史中，大陆在全球范围内漂移，周期性地聚集成超级大陆。 盘古大陆是其中最近的一个：在大西洋扩张之前，将美洲与欧洲和非洲连接起来的单一大陆。 盘古大陆之前可能存在更古老的超级大陆，名为罗迪尼亚（大约 9 亿年前）和努纳（大约 15 亿年前），它们都存在于原始生命的“元古代”时期。 尽管这些超级大陆有名称，但它们的大陆碎片的确切排列仍然不确定。 不管怎样，地质学家开始推测超大陆转变是否通常具有类似手风琴的运动模式（想象一下未来美洲会逆转航向并向东漂移以接近大西洋并重新与欧洲和非洲相撞），或者大陆是否环绕地球一周（想象一下美洲继续向西漂移以接近太平洋并与东亚和澳大利亚相碰撞，从而使旧的超级大陆转变） “由内而外”）。 这些想法有助于塑造我们对地球内部数十亿年演变的看法，并为最长时间尺度上的矿藏形成、古代气候记录和生物进化提供地理背景。该项目使用两种互补的实验室测量方法来确定大陆如何在地球表面移动：古地磁学——岩石记录的地磁场的古代记录；以及利用铀的放射性衰变对岩石年龄进行同位素测年。 该项目的重点是努纳和罗迪尼亚超大陆地块中人们最不了解的大陆碎片：西非克拉通。在西非，特别是摩洛哥的安提阿特拉斯山脉，地质认识的最新进展提供了将这两种方法应用于不同年龄的古代火山岩系统（“基性岩脉”）的机会，以对努纳和罗迪尼亚大陆进行更准确的重建，并发现地球超大陆转变的模式。 该项目将包括现场收集岩石样本、对这些样本进行实验室分析以及在同行评审期刊上发表结果。除了该项目的科学目标外，与该项目相关的重要社会成果还包括在重要的科学、技术、工程和数学（STEM）学科中培训下一代地球科学家；将项目成果纳入公共博物馆展示；与 K-12 公立学校教师一起开发教育模块。努纳和罗迪尼亚超级大陆构造的不确定性目前允许最终成员对长期全球地球动力学提出两种观点：超级大陆是否倾向于恢复到先前的构造，或者“从内到外”。 他们也有可能及时在这两种模式之间交替。 西非的古地理是所有主要前寒武纪克拉通中受限制最少的，之前假设的位于前泛古大陆超级大陆中部或沿其外围的位置对于上述争论至关重要。 该项目旨在对摩洛哥反阿特拉斯山脉前寒武纪内层的镁铁质岩墙群进行综合古地磁和地质年代学研究。 从这项研究中获得的高质量和精确年代的古地磁极将填补西非以及努纳和罗迪尼亚邻近地块的构造和运动学历史上的显着空白，并为超大陆过渡样式的辩论提供必要的事实依据。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智力价值和更广泛的评估进行评估，被认为值得支持。 影响审查标准。