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）沿着沿着海沟下降到地球内部，2）板块在大洋中脊扩张，大部分海底都是在那里形成的，3）浮力上涌，或地幔柱，其中热的和密度较低的物质从地球深处上升到表面，形成火山，如夏威夷群岛。这三个系统相互作用的地点，包括汤加海沟，劳弧后扩张中心，萨摩亚火山岛提供了独特的机会，调查这些竞争机制。在这项研究中，并列的萨摩亚羽和北方边缘的汤加劳俯冲系统是用来调查地幔流在板状羽设置，并了解如何独特的成分和热特征的羽流材料的分布。 该项目为研究生和本科生以及一名博士后研究员提供培训，利用一个跨学科项目调查汤加-劳-萨摩亚系统，该项目包括地震成像、海底熔岩地球化学分析和地球动力学建模。将在北方汤加-劳和萨摩亚区域部署30个海底地震仪和5个陆地地震仪（包括3个常设台站），为期18个月，从中获得地震观测数据。几种不同的地震成像技术将提供上地幔的三维速度模型，精确的地震位置将对板片撕裂和相关变形进行成像，地震速度随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个海山地点挖掘熔岩样本，以更好地了解进入汤加海沟北方的俯冲输入，目的是了解劳盆地富集地幔物质的分布情况。将对样品进行同位素组成分析，以确定Lau盆地非萨摩亚热点物质的可能来源，这对地幔流的地球化学解释至关重要。一系列的地球动力学模型将模拟各种可能配置的板块-羽流相互作用。利用模型中随时间变化的地幔流的综合历史，预测的热结构和地幔纹理可以直接与地震和地球化学观测进行比较。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。

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.