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，其中较温暖的物质上升到表面，而寒冷的构造板块则深入内部。了解这一过程对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，这些因素在整个地球历史中稳定了大气层，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站记录的地震数据，并结合对大洋板块分离的大洋中脊收集的岩石挥发物的地球化学估计，研究固体地球中的大规模对流和挥发路径。虽然地幔必须在这些位置上升，以取代板块的质量，因为它们的分歧，隆起通常被认为是小规模的，不一定与更大的整个地球对流系统。然而，最近的地震成像和研究人员自己的地球化学数据和地球物理数据之间的比较表明，在某些地区，大洋中脊下的隆起可能与下地幔相连，这对理解地球上的挥发物、挥发物的路径和丰度具有广泛的意义。一个外展计划将通过设计一个交互式数字工具来增加地球科学的多样性，该工具将探索和解释地球的深层挥发性循环及其与物理岩石样本的联系。它将被设计为各种级别，可供专家，导游，K-12学校团体，自我指导的学生，公众和在线探险家使用。该工具将通过大型便携式触摸屏界面在美国海洋样品库提供。罗得岛和伍兹霍尔海洋研究所，它们储存了许多本项目要研究的岩石样本。在过去五年（包括新型冠状病毒疫情），该等设施合共接待约15，000名访客。这些内容还将在WHOI探索博物馆的旋转展览部分展出，并将通过火山@URI托管的网站提供。最后，该项目将为2名研究生提供关于地球化学分析和全球地震分析的尖端方法的培训。水对地球上的生命至关重要。它也在研究地球内部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）将上地幔与下地幔从~410至~660 km深度分开，是地球水合循环的关键，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已被证明具有挑战性。地幔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。一般认为，洋脊相对独立于地球的大尺度全地幔对流模式。然而，洋中脊玄武岩（MORB）侵位期间，洋脊确实会从地幔中释放水。虽然MORB的水含量相对较低，但洋脊代表了地球上最长的连续板块边界，因此通过洋脊系统的水的总质量是相当大的。海脊也是了解上地幔含水量的一个窗口。研究人员对现有信息进行了一些初步比较，即全球地震模型和以前分析的海脊样本中汇编的含水量。 他们发现，在某些地点，含水量较高的MORB样品对应于地震观测值可能表明MTZ中水合作用增强的地点。他们还发现，许多海脊段的地球化学数据太少，无法限制任何趋势。这项初步工作是有希望的，需要更多的关注和调查。该项目由地球物理学、海洋地质学和地球物理学项目共同资助。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.