CSEDI: Whole-Mantle Convection and the Transition-Zone Water Filter

CSEDI：全地幔对流和过渡区水过滤器

• 批准号: 0330745
• 负责人: David Bercovici
• 金额: $ 78万
• 依托单位: Yale University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-07-01 至 2009-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0330745&HistoricalAwards=false
• 关键词: CSEDI; Whole; Mantle; Convection; Transition

A major question about the Earth's interior is why the mantle appearsboth well-mixed and unmixed at the same time. Geochemical analyses implythat the two main types of mantle convective upwellings (which createmid-ocean ridge basalts MORB and ocean-island basalts OIB, respectively)have distinct chemical signatures and thus come from different isolatedlayers in the mantle. However, seismological studies suggest thatcold downwellings (called subducting slabs) sink across the entiremantle and would therefore stir the mantle and destroy any layering.Thus there appears to be completely contradictory pieces of evidenceof how the mantle convects. However, it has been recently suggestedthat melting at 410 km depth in the mantle can act as a filter thatsequesters incompatible elements into the deep (sub-410km) mantle, butallows whole-mantle circulation of major components, thereby satisfyingboth geochemical and geophysical constraints. As most of the ambientupwelling mantle rises out of the high-water-solubility transitionzone into the low-solubility upper mantle above 410km, it becomeswater-supersaturated and undergoes dehydration melting that filtersout incompatible elements. The filtered solid phase supplies dry,depleted materials to the MORB source region. The filter, however,is suppressed for hotter, faster mantle plumes which therefore deliverenriched OIBs. This "water-filter" model raises many new questions: (1)What is the predicted structure of the putative melt layer at the 410km,and how can this be tested seismologically? (2) What is the influenceof the filter mechanism on mantle convection and chemical circulation?(3) What is the nature of hydrous melt at deep upper-mantle conditions?Answering these and a host of other important new questions demands aninterdisciplinary approach and therefore involves a team comprised ofa geodynamicist, an experimental mineral physicist, a seismologist anda geochemist.Broader impact:This project involves the education of two graduate students in a highlyinterdisciplinary project entailing geodynamics, mineral physics,seismology and geochemistry. The water-filter model also raises newquestions and fields of research that will drive interaction betweendisciplines and provide focus and hypothesis-testing for the largerobservational and experimental programs such as EarthScope, OMD (OceanMantle Dynamics) and COMPRES.

关于地球内部的一个主要问题是，为什么地幔在同一时间均匀混合和融合。 地球化学分析表明，两种主要类型的地幔对流上升（分别为createmid-ocean Ridge basalts Morb和Ocean-Island Basalts oib）具有不同的化学特征，因此来自大衣中不同的分离层。 然而，地震学研究表明，猫的倒塌通（称为俯冲板）沉入了整个壁炉，因此会搅动地幔并破坏任何分层。因此，似乎有完全矛盾的证据，证明了地幔对流的方式。 然而，最近有人认为，地幔中410 km的熔化可以充当过滤器，使得序列不兼容的元素进入深处（sub-410 km）地幔，但却可以使主要组成部分的全井球循环，从而满足地球化学和地球物理约束。 随着大多数环境地幔从高水溶性的过渡区升至低于410公里以上的低溶解度上地幔时，它变得饱和，并经历过滤脱水的脱水融化，从而过滤了不可能的元素。过滤后的固相供应干燥，耗尽的材料到MORB源区域。 然而，该过滤器被抑制，以使其更热，更快的地幔羽流，从而递送含有元素的OIB。 这种“水过滤器”模型提出了许多新问题：（1）假定熔体层在410公里处的预测结构是什么，如何在地震学上进行测试？ （2）滤波器机制对地幔对流和化学循环的影响是什么？（3）在深层通讯条件下液压熔体的性质是什么？回答这些问题以及许多其他重要的新问题需要一个学科的方法，因此参与一个团队由地球力学物理学家，地震学家和地球化学家组成。Boader的影响：该项目涉及在一个高度互差的项目中对两名研究生的教育，该项目涉及地球动力学，矿物质物理学，Seismology和Geochoctristion。 水过滤器模型还提出了新的研究和研究领域，这些研究将推动在学科的互动，并为较大的托管和实验计划（例如Earthscope，OMD（OMD）（OMD）（OMENMANTLE DYNALICS）和组合提供重点和假设测试。