Mesoarchean diamond-bearing sediments: implications for Archean continental roots and their surface expression

大陆地壳是地球上生命发展和维持的基础。大陆地壳，特别是古代大陆地壳，生产了世界上90%的黄金和铂金矿床，以及几乎所有已开采的钻石。古代大陆地壳在今天的地球上显然是稳定的，并且通常比年轻的地壳块具有更深的地幔根。然而，古代大陆地壳是如何形成的，也许更重要的是，是如何稳定下来的，这仍然是地球科学中的一个悬而未决的问题。这个项目将通过利用最近发现的保存在古代沉积岩样本中的28.5亿年前的钻石来帮助解决这个问题。钻石是对大陆深层根部取样的最佳工具，钻石所含的沉积物保存了地球历史上大陆的海拔和表面的记录。这些小钻石可能是地球上最古老的钻石，它们的化学特征记录了大陆地壳最早的根是如何形成的。这个项目将寻找更多这些有价值的深层大陆根记录，同时也调查现在发现它们的沉积岩。沉积岩记录了它们沉积时的表面特征，因此这种深度和表面结合的研究将有助于解决诸如：早期地球是海洋世界吗？大陆的根是在大陆升到海平面以上之前形成的吗？古代大陆在变得坚硬和稳定之前，早期是松散和可塑的吗？这项研究的结果将作为输入数据，供科学家们试图了解古代大气的组成、古代生物过程以及地球上形成的矿床有多重要。参与这项提议的研究小组最近在加拿大地盾中发现了保存在28.5亿年前的沉积物中的碎屑钻石。太古宙钻石在这一时期在地球表面的存在及其详细的地球化学特征，为大陆地壳保存区域的形成和时间整合稳定性提供了关键证据。该团队将评估这些古老钻石的流行程度、位置和地幔居住年龄，以及它们的地球化学特征，以测试岩石圈深部地幔根形成时间的模型，以及它们对大规模克拉通形成的意义。研究小组还将评估现在含有古钻石的沉积物，包括它们的集水区大小（古流域的大小）、集水区年龄分布和沉积环境。这些输入将有助于了解在地球历史的早期是否形成了显著的大陆高地，这可能是由于大陆根系的稳定造成的。本提案中的工作将使用单一样品集和专门的野外活动来解决克拉通形成和大陆稳定性的两个主要方面。研究小组将使用浮动飞机对加拿大北部偏远地区的岩石进行取样，然后在美国和加拿大的实验室进行最先进的化学分析。对整个地球历史上大陆地壳生命周期的全面了解对地球科学界具有广泛的科学意义，包括帮助理解大气如何变得富含氧气以及地球表面的生命如何进化。这一提议也将导致大量古代钻石的收集，可以在未来的工作中进行研究。此外，古克拉通块体拥有地球经济的铂、金和钻石的很大一部分，使其成为经济上重要的地质特征。重要的是，古代沉积物中碎屑钻石的普遍程度在很大程度上是未知的，因此这个项目的结果可能会推动全球类似沉积物的经济活动（勘探和资源开发）。该项目将资助博士的培训，他们也将接触到地球科学行业的许多部门，包括学术界，政府调查，经济勘探和采矿以及许多类型的先进分析技术。钻石研究和早期地球地质学一样，是科学媒体和公众非常关注的研究课题。我们将尽一切努力与科普媒体合作，扩大项目成果的影响力和公众参与度。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知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The continental crust is fundamental to the development and sustainment of life on Earth. Continental crust, and in particular ancient continental crust, produces 90% of the world’s gold and platinum deposits and nearly all of the mined diamonds. Ancient continental crust is clearly stable on Earth today and often has a much deeper mantle root than younger crustal blocks. Yet, how ancient continental crust formed and, perhaps more importantly, was stabilized, remains an outstanding question in the Geosciences. This project will help to address this question by making use of recent discoveries of 2.85 billion-year-old diamonds preserved in ancient sedimentary rock samples. Diamonds are the best available tools to sample the deep roots of continents, and the sediments they are contained within preserve a record of the elevation and surface of the continents back in Earth history. These small diamonds are likely some of the oldest diamonds on Earth, and their chemical signatures record how the earliest roots of the continental crust formed. This project will look for more of these valuable records of the deep continental root, while also investigating the sedimentary rocks where they are now found. Sedimentary rocks record the surface features at the time they were deposited, so this combined deep-and-surface study will help address questions such as: Was the early Earth an ocean world? Did the roots of continents form first before continents rose above sea level? Were ancient continents loose and malleable early in their life before they became rigid and stable? The outputs of this research will serve as input data for scientists trying to understand the composition of the ancient atmosphere, ancient biological processes, and how important mineral deposits were formed on Earth. The research team involved in this proposal recently discovered detrital diamonds preserved in ca. 2.85 billion-year-old sediments in the Canadian shield. The presence of Archean diamonds at Earth’s surface during this time interval, and their detailed geochemical signatures, contain key evidence for the formation and time-integrated stability of regions of preserved continental crust. The team will evaluate the prevalence, location, and mantle-residence ages of these ancient diamonds, as well as their geochemical signatures to test models for the timing of the formation deep lithospheric mantle roots and their significance for large scale craton formation. The team will also evaluate the sediments that now contain the ancient diamonds including their catchment size (size of the ancient watershed), catchment age distributions, and the depositional environment. These inputs will help understand if significant continental elevation was formed in the very early in Earth history, potentially due to continental root stabilization. The work in this proposal will address two major aspects of craton formation and continental stability, using a single sample set and a dedicated field campaign. The research team will use float planes to sample rocks in the remote regions of Northern Canada and will then conduct state-of-the-art chemical analyses in laboratories in the US and Canada. A full understanding of the life cycle of continental crust throughout Earth history has broad scientific implications for the geoscience community, including helping to understand how the atmosphere became rich in oxygen and how life evolved on the surface of the Earth. This proposal will also result in a large collection of ancient diamonds which can be studied in future work. Additionally, ancient cratonic blocks host a large fraction of Earths economic Pt, Au, and diamonds making them economically important geologic features. Importantly, the prevalence of detrital diamonds in ancient sediments is largely unknown, such that the results of this project may drive economic activities (exploration and resource development) in similar sediments globally. This project will fund training of a PhD who will also be exposed to many sections of the geoscience industry, including academia, governmental surveys, and economic exploration and mining as well as many types of advanced analytical techniques. Diamond research, as well as the geology of the early Earth, is a research topic that is popular with the science media and general public. Every effort will be made to engage with the popular science media to expand the influence and public engagement with the results of this project.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.