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.

尽管在过去的几年中，我们对地球深层地幔的动态和演变的理解取得了显着进步，但一个主要方面变得越来越有争议。热点火山是由深lum污水喂养的吗？三十年来，这一直是标准模型的中心宗旨，但现在与“自上而下”模型形成鲜明对比，该模型严格地通过表面板的裂缝构造构造了高地幔的热点火山。虽然夏威夷热点链是羽流模型的“原型”，但经常将萨摩亚链作为自上而下模型的证据。萨摩亚的最新研究表明，虽然骨折构造在火山主义中起着重要作用，但它只是羽流驱动的热点的“末端游戏”。该项目使用萨摩亚热点和邻近的汤加俯冲带的独特并置，以阐明这种相互作用的动力学，并对有关羽毛的辩论有了批判性的理解。当汤加平板迅速向东滚回去时，它迫使平板和太平洋板之间的铰链断层向东繁殖。该项目的中心论点是，这种滚动后向北向北的“逃脱”从平板下方逃脱，迫使萨摩亚羽流逐渐向北行驶，留下了一系列echelon火山层。同时，汤加太平洋铰链的繁殖以及地幔的相关返回流入后弧区，产生了恢复活力的火山，这与萨摩亚热点谱系相连。这项研究包括一个多学科的多机构动态学家（M. Billen，UC Davis和C. Kincaid，Uri），Seismologist（M. Behn和J. Collins，Whoi），地球化学家和矿物质学家（S. Hart和G. Hirth，Whoi）。 3-D计算建模和实验“油箱”建模用于研究平板回滚和（假定的）羽流导管的动态相互作用。沿萨摩亚链部部署了四个地震站，并将与现有的永久台阶一起进行进行剪切波分裂测量。在数值和实验流建模的背景下，解释了对地震各向异性的这些区域观察（以及来自斐济和LAU背面的公开值），并限制了汤加平板周围地幔流的模式。来自这些相同站点的PS和SP接收器功能提供了岩石圈厚度和410-660 km过渡区的厚度的估计。 （推定的）羽状板相互作用的性质正在划定，并结合了构造特征的地球化学和映射，允许在板骨折模型和羽流驱动的热点模型之间进行区分。这些研究提供了对我们萨摩亚 - 汤加（Samoa-Tonga）互动概念中特定问题的明确检验。涉及所有参与者的会议定于2007年6月8日在伍兹霍尔海洋学院举行。这些学生还将在来年对其他机构进行短期访问。频繁的电话会议和视频会议用于进一步增强学生的参与。鼓励学生参加2008年的苹果酒夏季计划，以此为他们的学习提供背景和广度。晶状体偏爱方向的运动学模型已集成到Citcom 3-DContraction代码中，这些模型将通过地球动力学的计算基础架构提供给整个社区。在更广泛的外展战线中，第一次前往萨摩亚的旅行服务于2007年7月上旬举行。计划访问Savai`i和Ta`U上的高中，并计划在科学课程上，将重点放在火山，羽毛和板块构造上。鉴于当地学校围绕着精美的火山地形，学生和老师都将进行非正式的半天实地考察。