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.

尽管在过去几年中，我们对地球深部地幔的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经变得越来越有争议。热点火山活动是否由地幔柱提供？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”的模型形成对比，该模型严格从上地幔通过地表板块的断裂构造推导出热点火山作用。虽然夏威夷热点链是羽流模型的“原型”，但萨摩亚链经常被引用作为自上而下模型的证据。最近在萨摩亚的研究表明，虽然断裂构造在火山活动中发挥了重要作用，但它只是羽流驱动热点的“最后阶段”。该项目利用萨摩亚热点和邻近的汤加俯冲带的独特并置来阐明这种相互作用的动态，并为更普遍地关于羽流的辩论提供重要的理解。当汤加板块快速向东滚动时，它迫使板块和太平洋板块之间的枢纽断层向东传播。该项目的中心论点是，这种回滚驱动地幔从板块下方向北流动“逃逸”，迫使萨摩亚地幔柱逐步向北移动，留下一系列雁列状火山线性构造。与此同时，传播的汤加-太平洋枢纽，并与返回流的地幔到弧后地区，产卵复活的火山活动，是偶然连续的萨摩亚热点线性。这项研究包括一个多学科多机构的动力学家（M。Billen，UC Davis和C. Kincaid，URI），地震学家（M。贝恩和J.柯林斯，WHOI），地球化学家和矿物物理学家（S。哈特和G. Hirth，WHOI）。三维计算模型和实验“坦克”模型正在被用来研究动态相互作用的板坯回滚和（假定）羽状导管。沿着萨摩亚链部署了四个地震观测站，将与现有的常设观测站一起进行剪切波分裂测量。这些区域观测的地震各向异性（沿着与斐济和劳弧后公布的值）的数值和实验流动模拟的背景下进行解释，并约束的模式，地幔流周围的汤加板。来自这些台站的Ps和Sp接收器功能提供了岩石圈厚度和410-660 km过渡带厚度的估计。（假定的）地幔柱板块相互作用的性质正在划定，并结合地球化学和构造特征的绘图，允许板块断裂模型和地幔柱驱动的热点模型之间的区别。这些研究对我们的萨摩亚-汤加互动概念中明确提出的一系列具体问题进行了明确和直接的测试，三个机构的研究生都参与了这一项目，并积极参与项目的各个方面。所有与会者已定于2007年6月8日在伍兹霍尔海洋研究所举行一次会议。此外，我们亦会在来年接待学生到其他院校作短期访问。频繁的电话会议和视频会议被用来进一步提高学生的参与。鼓励学生参加2008年CIDER暑期课程，作为提供背景和广度，他们的研究的一种方式。网格优先取向的运动学模型正在被纳入CITCOM三维对流代码，这些模型将通过地球动力学计算基础设施提供给整个社区。在更广泛的外联方面，计划于2007年7月初首次前往萨摩亚为地震台站提供服务;计划访问萨瓦伊和塔乌的中学，并安排一天的科学课，重点是火山、羽流和板块构造。由于当地学校周围有精美的火山地形，学生和教师将进行非正式的半天实地考察。