Collaborative Research: CSEDI--The Dynamics of Plume-Trench Interaction: Samoa-Tonga

合作研究：CSEDI--羽流-海沟相互作用的动力学：萨摩亚-汤加

• 批准号: 0652924
• 负责人: Magali Billen
• 金额: $ 13.92万
• 依托单位: University of California-Davis
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-06-01 至 2010-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0652924&HistoricalAwards=false
• 关键词: Collaborative; Research; CSEDI; Dynamics; Plume

Despite remarkable advances over the past few years in our understanding of the dynamics and evolution of Earth's deep mantle, one major aspect has become increasingly contentious. Is hotspot volcanism fed by deep mantle plumes or not? This has been a central tenet of the Standard Model for three decades, but is now contrasted with a "top down" model that derives hot spot volcanism strictly from the upper mantle, via fracture tectonics of the surface plates. While the Hawaiian hotspot chain is the "archetype" for the Plume model, the Samoan chain is cited frequently as evidence for the Top Down model. Recent studies in Samoa show that, while fracture tectonics plays an important role in the volcanism, it is only the "end-game" of a plume-driven hotspot. This project uses the unique juxtaposition of the Samoa hotspot and adjacent Tonga subduction zone to illuminate the dynamics of this interaction, and to contribute critical understanding to the debate about plumes more generally. As the Tonga slab rolls back rapidly to the east, it forces an eastward propagation of the hinge fault between the slab and the Pacific plate. The central thesis of this project is that this roll-back drives a northward flow of mantle "escaping" from beneath the slab, forcing the Samoa plume to step progressively northward, leaving behind a series of en echelon volcanic lineaments. Concomitantly, the propagation of the Tonga-Pacific hinge, and associated return flow of mantle into the back-arc region, spawns rejuvenated volcanism that is incidentally contiguous with the Samoan hotspot lineament. This study comprises a multi-disciplinary multi-institutional group of dynamicists (M. Billen, UC Davis, and C. Kincaid, URI), seismologists (M. Behn and J. Collins, WHOI), a geochemist and a mineral physicist (S. Hart and G. Hirth, WHOI). 3-D computational modeling and experimental "tank" modeling is being used to study the dynamic interaction of slab rollback and the (putative) plume conduit. Four seismic stations have been deployed along the Samoa chain and, in conjunction with existing permanent stations, will be used to make shear-wave splitting measurements. These regional observations of seismic anisotropy (along with published values from Fiji and the Lau back-arc) are interpreted in the context of the numerical and experimental flow modeling, and constrain the pattern of mantle flow around the Tonga slab. Ps and Sp receiver functions from these same stations provide estimates of lithospheric thickness, and thickness of the 410-660 km transition zone. The nature of (putative) plume-plate interaction is being delineated and, combined with the geochemistry and mapping of tectonic features, allows distinctions between plate-fracture models and plume-driven hotspot models. These studies provide clear and direct tests of the specific set of questions explicit in our concept for the Samoa-Tonga interaction.Graduate students from each of the three institutions are involved and are active participants in all aspects of the project. A meeting involving all participants has been scheduled for June 8, 2007 at the Woods Hole Oceanographic Institution. The students will also be hosted for short visits to the other institutions in the coming year. Frequent conference calls and video-conferences are used to further enhance the student participation. The students are encouraged to attend the 2008 CIDER Summer Program, as a way of providing context and breadth to their studies. Kinematic models for lattice-preferred orientation are being integrated into the CITCOM 3-Dconvection code, and these will be made available to the entire community through the Computational Infrastructure for Geodynamics. On a broader outreach front, the first trip to Samoa to service the seismic stations has been scheduled for early July 2007; visits to high schools on Savai`i and Ta`u are planned, with a day of science classes that will focus on volcanoes, plumes and plate tectonics. Given the exquisite volcanic terrain surrounding the local schools, informal half-day field trips will be run for both students and teachers.

尽管过去几年我们对地球深部地幔动力学和演化的理解取得了显着进展，但其中一个主要方面已变得越来越有争议。热点火山活动是否由深部地幔羽流供给？三十年来，这一直是标准模型的核心原则，但现在与“自上而下”模型形成鲜明对比，“自上而下”模型通过表面板块的断裂构造严格从上地幔导出热点火山活动。虽然夏威夷热点链是 Plume 模型的“原型”，但萨摩亚热点链经常被引用作为自上而下模型的证据。萨摩亚最近的研究表明，虽然断裂构造在火山活动中发挥着重要作用，但这只是羽流驱动热点的“最终游戏”。该项目利用萨摩亚热点和邻近汤加俯冲带的独特并置来阐明这种相互作用的动态，并为更广泛地关于羽流的争论提供批判性的理解。当汤加板块迅速向东滚动时，它迫使板块与太平洋板块之间的铰接断层向东传播。该项目的中心论点是，这种回滚驱动了地幔从板块下方“逃逸”向北流动，迫使萨摩亚地幔柱逐渐向北移动，留下了一系列呈阶梯状的火山轮廓。与此同时，汤加-太平洋铰链的扩展以及与之相关的地幔回流到弧后区域，产生了与萨摩亚热点地貌相邻的复兴的火山活动。这项研究由一个多学科、多机构的小组组成，其中包括动力学家（M. Billen，加州大学戴维斯分校和 C. Kincaid，URI）、地震学家（M. Behn 和 J. Collins，WHOI）、地球化学家和矿物物理学家（S. Hart 和 G. Hirth，WHOI）。 3-D 计算模型和实验“坦克”模型被用来研究板坯回滚和（假定的）羽流管道的动态相互作用。沿萨摩亚链部署了四个地震台，并将与现有的永久台一起用于进行剪切波分裂测量。这些地震各向异性的区域观测（以及斐济和劳弧后公布的值）在数值和实验流模型的背景下进行了解释，并限制了汤加板片周围地幔流的模式。来自这些相同站点的 Ps 和 Sp 接收器函数提供了岩石圈厚度以及 410-660 km 过渡带厚度的估计。 （假定的）羽流-板块相互作用的本质正在被描述，并与地球化学和构造特征绘图相结合，可以区分板块-断裂模型和羽流驱动的热点模型。这些研究为萨摩亚-汤加互动概念中明确的一组特定问题提供了清晰和直接的测试。来自三个机构的研究生都参与并积极参与该项目的各个方面。所有参与者参加的会议定于 2007 年 6 月 8 日在伍兹霍尔海洋研究所举行。来年，学生们还将被接待对其他机构进行短期访问。频繁的电话会议和视频会议进一步提高了学生的参与度。我们鼓励学生参加 2008 年 CIDER 暑期项目，以此为他们的学习提供背景和广度。晶格优先方向的运动学模型正在集成到 CITCOM 3-D对流代码中，并且这些模型将通过地球动力学计算基础设施向整个社区提供。在更广泛的外展方面，首次前往萨摩亚为地震台站提供服务已计划于 2007 年 7 月初进行；计划参观萨瓦伊岛和塔乌岛的高中，并安排一天的科学课程，重点关注火山、羽流和板块构造。鉴于当地学校周围有精致的火山地形，将为学生和教师举办非正式的半天实地考察。