Collaborative Research: Interactions Between the Tonga-Lau Subduction System and the Samoan Plume

固体地球科学的一个基本目标是提高我们对地幔对流驱动的地球内部演化的理解。地幔对流系统有三个主要组成部分：1)俯冲，其中一个构造板块(板块)沿着大洋海沟下降到地球内部，2)板块在大洋中脊展开，大部分海底就是在那里形成的，3)浮力上涌，或称地幔羽流，在那里，热的和密度较低的物质从地球深处上升到地表，形成像夏威夷群岛那样的火山。这三个系统相互作用的地点--包括汤加海沟、刘弧后扩张中心和萨摩亚火山岛--为研究这些相互竞争的机制提供了独特的机会。在这项研究中，萨摩亚热柱与汤加-刘俯冲系统北缘的并置被用来研究板状-热柱背景下的地幔流动，并了解热柱物质独特的成分和热特征是如何分布的。该项目为研究生和本科生以及博士后研究员提供培训。一个跨学科项目，包括地震成像、海底熔岩地球化学分析和地球动力学建模，用于调查汤加-刘-萨摩亚系统。将在汤加-刘和萨摩亚北部地区部署30台海底地震仪和5台陆地地震仪(包括3个常设台站)，为期18个月进行地震观测。几种不同的地震成像技术将提供上地幔的三维速度模型，精确的地震位置将成像板片撕裂及其相关变形，而地震速度沿方向的变化将对地幔流动提供约束。将在汤加海沟以东的10个海山位置挖掘熔岩样品，以更好地了解向汤加海沟北部的俯冲输入，目的是了解刘盆地富集地幔物质的分布。将对样品进行同位素组成分析，以确定刘盆地非萨摩亚热点物质的可能来源，这对地幔流动的地球化学解释至关重要。一系列地球动力学模型将模拟具有各种可能构型的平板-羽流相互作用。使用模型中随时间变化的地幔流动的综合历史，预测的热结构和地幔结构可以直接与地震和地球化学观测进行比较。这一奖项反映了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。

A fundamental goal of solid earth science is to improve our understanding of the Earth’s interior evolution, which is driven by mantle convection. There are three primary components of the mantle convection system: 1) subduction where one tectonic plate (slab) descends into the Earth’s interior along an oceanic trench, 2) plate spreading at mid-ocean ridges where the majority of seafloor is created, and 3) buoyant upwelling, or mantle plumes, where hot and less dense materials rise from the deep earth to the surface to create volcanoes like the Hawaiian islands. Locations where these three systems interact—including the Tonga oceanic trench, Lau back-arc spreading centers, and Samoa volcanic islands—provide unique opportunities to investigate these competing mechanisms. In this study, the juxtaposition of the Samoan plume and the northern edge of the Tonga-Lau subduction system is used to investigate mantle flow in a slab-plume setting, and to understand how the distinctive compositional and thermal characteristics of plume materials are distributed. The project provides training for graduate and undergraduate students and a postdoctoral investigator.An interdisciplinary project, consisting of seismic imaging, geochemical analysis of submarine lavas, and geodynamic modeling, is used to investigate the Tonga-Lau-Samoa system. Seismic observations will be obtained from an 18-month deployment of 30 Ocean Bottom Seismographs (OBSs) and 5 land seismometers (including 3 permanent stations) in the northern Tonga-Lau and Samoa regions. Several different seismic imaging techniques will provide 3-D velocity models of the upper mantle, precise earthquake locations will image the slab tear and associated deformation, and the variation of seismic velocity with direction will provide constraints on mantle flow. Lava samples will be dredged at 10 seamount locations east of the Tonga Trench to better understand subduction inputs into the northern Tonga Trench with the goal of understanding the distribution of enriched mantle material in the Lau Basin. The samples will be analyzed for isotopic compositions allowing identification of possible sources of non-Samoan hotspot materials in the Lau Basin, which is critical for geochemical interpretations of mantle flow. A series of geodynamic models will simulate slab-plume interactions with a variety of possible configurations. Using the integrated history of time-dependent mantle flow in the models, the predicted thermal structure and mantle textures can be directly compared with seismic and geochemical observations.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.