Collaborative Research: Geophysical and geochemical investigation of links between the deep and shallow volatile cycles of the Earth

自数十亿年前形成以来，地球一直通过对流慢慢冷却，在对流中，较热的物质上升到表面，寒冷的构造板块深入内部。了解这一过程对于一系列问题都很重要，例如确定驱动板块构造维持深水和碳循环的因素，以稳定地球历史上的大气、水圈和气候。这与社会特别相关，因为板块构造过程是地震和火山等灾害背后的驱动力，也因为我们的气候和大气使地球适合居住。该项目利用全球地震台记录的地震数据，结合对海洋板块发散的大洋中脊收集的岩石挥发分的地球化学估计，研究了固体地球中的大范围对流和挥发路径。尽管地幔必须在这些位置上升，以取代板块发散时的质量，但上升流通常被认为规模较小，不一定与更大的整个地球对流系统有关。然而，最近的地震成像以及研究人员自己对地球化学数据和地球物理数据的比较表明，在某些地区，大洋中脊下的上升流可能与下地幔相连，这对了解地球上的挥发性物质、它们的路径和丰度具有广泛的意义。一项推广计划将通过设计一种交互式数字工具来增加地球科学的多样性，该工具探索和解释地球的深度不稳定循环及其与物理岩石样本的联系。它将为不同的层次设计，可供专家、导游、K-12学校团体、自学学生、公众和在线探险者使用。该工具将通过位于美国罗德岛大学和伍兹霍尔海洋研究所的海洋样品储存库中的大型便携式触摸屏界面提供，这两个储存库存储了许多将由该项目研究的岩石样品。在过去5年中，这些设施总共接待了约15,000名游客，其中包括新冠肺炎大流行。内容还将在WHOI探索博物馆的轮换展览区展出，并将通过Volcano@URI托管的网站上提供。最后，该项目将为2名研究生提供地球化学分析和全球地震分析尖端方法方面的培训。水对地球上的生命是必不可少的。它还在研究地球深部及其演化方面发挥着重要作用。它被认为是板块构造存在、大陆形成、火山活动和地震发生的重要因素。地幔过渡带是地球水化循环的关键，因为它被认为具有储存海洋水的能力(S)，它将上下地幔从410到660公里的深度分开。然而，事实证明，确定过渡区水化的确切位置和路径是具有挑战性的。热柱和俯冲带被认为是上地幔和下地幔之间水化作用的主要通道。山脊通常被认为是相对独立于地球大规模的全地幔对流模式的。然而，在大洋中脊玄武岩(MORB)侵位过程中，山脊确实从地幔释放出水。尽管MORB的水分含量相对较低，但海脊代表着地球上最长的连续板块边界，因此通过海脊系统的水的总质量是相当大的。海脊也是了解上地幔大部分水分含量的一个可接近的窗口。研究人员对现有信息进行了一些初步比较，即全球地震模型和先前分析的山脊样本汇编的水分含量。他们发现，在某些地点，含水率较高的MORB样本对应于地震观测可能表明MTZ水合作用增强的地点。他们还发现，许多山脊段的地球化学数据太少，无法约束任何趋势。这项初步工作是有希望的，需要更多的关注和调查。该项目由地球物理、海洋地质学和地球物理项目共同资助。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Since its formation billions of years ago, Earth has been slowly cooling via convection, where warmer material rises to the surface and cold tectonic plates plunge deep into the interior. Understanding this process is important for a wide range of problems, such as determining the factors that drive plate tectonics to sustaining deep water and carbon cycles that stabilize the atmosphere, hydrosphere, and climate throughout Earth’s history. This is particularly relevant for society, both because plate tectonic processes are the driving forces behind hazards such as earthquakes and volcanoes and because our climate and atmosphere make Earth habitable. This project studies large scale convection and volatile pathways in the solid Earth by using earthquake data recorded at global seismic stations paired with geochemical estimates of volatiles from rocks collected at mid-ocean ridges where oceanic plates are diverging. Although the mantle must rise in these locations to replace the mass of the plates as they diverge, the upwellings are typically considered to be small in scale, not necessarily tied to the larger whole Earth convective system. However, recent seismic imaging and the researcher's own comparisons between geochemical data and geophysical data suggest that in some regions upwellings beneath mid-ocean ridges may connect to the lower mantle with broad implications for the understanding of volatiles on Earth, their pathways, and abundances. An outreach program will increase diversity in the Earth Sciences by designing an interactive digital tool that explores and explains Earth’s deep volatile cycle and its connection to physical rocks samples. It will be designed for various levels, useable by experts, tour guides, K-12 school groups, self-directed students, the public, and explorers online. The tool will be delivered via large portable touchscreen interfaces in the marine sample repositories at U. Rhode Island and Woods Hole Oceanographic Institution, which store many of the rock samples to be studied by this project. Together the facilities reached ~15,000 visitors in the past 5 years, which included the COVID pandemic. The content will also be displayed at the WHOI Discovery Museum in the rotating exhibit section and will be made available on a website hosted through Volcano@URI. Finally, the project will provide training for 2 graduate students in cutting-edge methodologies in geochemical analyses and global seismic analyses. Water is essential to life on Earth. It also plays a large role in studies of Earth’s deep interior and its evolution. It is thought to be an important factor in the existence of plate tectonics, the formation of the continents, and the initiation of volcanism and earthquakes. The mantle transition zone (MTZ), which separates the upper from the lower mantle from ~410 to ~660 km depth, is key to Earth’s hydration cycle in that it is thought to have the capacity to store ocean(s) of water. Yet, determining the exact locations and pathways of the hydration across the transition zone has proven challenging. Plumes and subduction zones are thought to be the main conduits of hydration between the upper and the lower mantle. Ridges are typically assumed to be relatively independent of Earth’s large-scale whole mantle convection patterns. However, ridges do release water from the mantle during mid-ocean ridge basalt (MORB) emplacement. Although MORB water contents are relatively low, ridges represent the longest continuous plate boundaries on the planet, and so the total mass of water passing through the ridge system is substantial. Ridges also represent an accessible window into the water content of much of the upper mantle. The researchers have made some preliminary comparisons of available information, namely global seismic models and compiled water contents from previously analysed ridge samples. They find that in some locations MORB samples with higher water content correspond to locations where seismic observables may suggest enhanced hydration in the MTZ. They also find many ridge segments have too little geochemical data to constrain any trend. This preliminary work is promising and demands additional attention and investigation. This project is co-funded by the Geophysics and Marine Geology and Geophysics programs.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.