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: 0652707
• 负责人: Stanley Hart
• 金额: $ 36.52万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-06-01 至 2012-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0652707&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进化的理解取得了显著进展，但有一个主要方面的争议越来越大。热点火山活动是否由深部地幔柱提供？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，该模型通过地表板块的断裂构造，严格地从上地幔导出热点火山活动。夏威夷热点链是羽流模型的“原型”，而萨摩亚热点链则经常被引用为自顶向下模型的证据。萨摩亚最近的研究表明，虽然断裂构造在火山活动中起着重要作用，但它只是羽流驱动的热点的“终局”。该项目利用萨摩亚热点和邻近的汤加俯冲带的独特并置，阐明了这种相互作用的动力学，并为更广泛地了解羽流的争论提供了关键的理解。当汤加板块迅速向东滚动时，它迫使板块和太平洋板块之间的铰链断层向东扩展。该项目的中心论点是，这种回滚推动地幔从板块下方“逃逸”向北流动，迫使萨摩亚火山柱逐渐向北移动，留下一系列雁梯队火山地貌。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地区，产生了与萨摩亚热点地区毗邻的重新焕发活力的火山活动。这项研究由多学科、多机构的动力学家（M. Billen, UC Davis，和C. kinkaid， 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）组成。利用三维计算模型和实验“槽”模型研究了平板回滚与（假定的）羽流管道的动态相互作用。沿萨摩亚岛链已经部署了四个地震台站，它们将与现有的永久台站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（以及斐济和劳弧后的公布值）在数值和实验流动模型的背景下进行了解释，并约束了汤加板块周围的地幔流动模式。来自这些相同台站的Ps和Sp接收函数提供了岩石圈厚度和410-660 km过渡带厚度的估计。（假定的）羽流-板块相互作用的性质正在被描绘出来，结合地球化学和构造特征的测绘，可以区分板块断裂模型和羽流驱动的热点模型。这些研究为我们关于萨摩亚-汤加相互作用的概念中明确提出的一系列具体问题提供了明确和直接的检验。来自这三所院校的研究生都积极参与到项目的各个方面。所有参与者将于2007年6月8日在伍兹霍尔海洋研究所举行会议。学生亦会在来年获邀到其他院校作短期访问。经常使用电话会议和视频会议，以进一步提高学生的参与度。我们鼓励学生参加2008年CIDER暑期项目，为他们的学习提供背景和广度。格优选方向的运动学模型正在集成到CITCOM 3-Dconvection代码中，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。在更广泛的外联方面，计划于2007年7月初第一次前往萨摩亚为地震台站提供服务；他们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，重点是火山、羽流和板块构造。考虑到当地学校周围精致的火山地形，学生和老师将进行非正式的半天实地考察。