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，地球一直在通过对流缓慢冷却，在对流中，较热的物质上升到表面，而较冷的构造板块深入到内部。了解这一过程对于解决一系列问题都很重要，比如确定驱动板块构造以维持深水和碳循环的因素，这些因素稳定了整个地球历史上的大气、水圈和气候。这对社会来说尤其重要，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。本项目利用全球地震台站记录的地震数据，结合海洋板块分叉处大洋中脊收集的岩石挥发物的地球化学估计，研究固体地球上的大尺度对流和挥发物路径。虽然这些地方的地幔必须上升，以取代板块分离时的质量，但上升流通常被认为规模很小，不一定与更大的整个地球对流系统有关。然而，最近的地震成像和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，洋中脊下的上升流可能与下地幔相连，这对理解地球上的挥发物、挥发物的途径和丰度具有广泛的意义。一个拓展项目将通过设计一个交互式数字工具来探索和解释地球的深层挥发循环及其与物理岩石样本的联系，从而增加地球科学的多样性。它将为不同的层次设计，可供专家、导游、K-12学校团体、自主学生、公众和在线探险家使用。该工具将通过罗德岛大学和伍兹霍尔海洋研究所海洋样本储存库中的大型便携式触摸屏界面交付，该储存库存储了该项目要研究的许多岩石样本。在过去的5年里，这些设施共接待了约1.5万名游客，其中包括COVID大流行。这些内容还将在WHOI发现博物馆的轮流展览部分展出，并将在Volcano@URI主办的网站上提供。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的前沿方法培训。水对地球上的生命是必不可少的。它还在研究地球深处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（MTZ）将上地幔和下地幔从~410到~660公里的深度分开，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。然而，确定过渡区水合作用的确切位置和途径被证明是具有挑战性的。地幔柱和俯冲带被认为是上、下地幔水化作用的主要通道。脊通常被认为相对独立于地球大尺度的整个地幔对流模式。然而，在洋中脊玄武岩（MORB）侵位期间，脊确实从地幔释放水分。虽然中北缘水含量相对较低，但脊线代表了地球上最长的连续板块边界，因此通过脊线系统的水的总质量是可观的。山脊也代表了一个了解大部分上地幔含水量的窗口。研究人员已经对现有的信息进行了一些初步的比较，即全球地震模型，并从之前分析过的山脊样本中收集了水的含量。他们发现，在某些地方，具有较高含水量的MORB样品对应于地震观测可能表明MTZ水化作用增强的位置。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。该项目由地球物理和海洋地质与地球物理项目共同资助。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。

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.