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Cratonic mantle eclogites as palaeo-dynamic archives

克拉通地幔榴辉岩作为古动力档案

基本信息

批准号：
327589446
负责人：
Dr. Sonja Aulbach
金额：
--
依托单位：
Abteilung Petrologie und Geochemie
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2017
资助国家：
德国
起止时间：
2016-12-31 至 2021-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/327589446?language=en
关键词：
Cratonic mantle eclogites palaeo dynamic

项目摘要

Mineralogical, elemental and isotopic data show that most eclogite xenoliths, which sample the mantle lithosphere of ancient continental cores, have low-pressure protoliths that were emplaced in palaeo-ocean floors after decompression melting beneath spreading ridges. Like modern mid-ocean ridge basalts, they are therefore probes of the chemical, thermal and redox state of the uppermost convecting mantle (UCOM). Subsequent recycling and metamorphism led to interaction between various oceanic slab components and loss of a partial melt that may have contributed to continental crustal (CC) growth. As rare samples of Archaean and Proterozoic oceanic crust, mantle eclogites may therefore harbour invaluable information on various aspects of palaeo-geodynamics that still awaits full exploitation. The groundwork having been laid for recognising primary and secondary compositional signatures related to their complex multi-stage evolution, this study aims to (1) Investigate the variegated origins of large mantle eclogite suites from different cratons and tectonic settings, using an extensive list of major and trace elements, complemented by radiogenic and stable isotopes and Fe3+/Fe2+ analyses; (2) Use the least differentiated and modified samples to provide new constraints on the chemical, oxidation and thermal state of the ancient UCOM, which strongly affect geodynamics and chemical cycles; (3) Test the link between melt loss from mantle eclogites and regional CC formation from a compositional and chronological perspective. Investigation of eclogite xenoliths from the Colorado Plateau, which were part of the well-studied modern ocean floor subducted as part of the Farallon plate and represent unique modern analogues of ancient eclogites, will allow ascertaining that ancient mantle eclogites can reliably probe the UCOM through time.

矿物学、元素和同位素数据表明，大多数榴辉岩捕虏体，样品的地幔岩石圈的古大陆核，具有低压原岩，是在扩张脊下减压熔融后侵位在古洋底。与现代洋中脊玄武岩一样，它们也是最上层对流地幔（UCOM）化学、热和氧化还原状态的探测器。随后的再循环和变质作用导致了各种大洋板块成分之间的相互作用，并导致了可能有助于大陆地壳（CC）生长的部分熔融的损失。地幔榴辉岩作为太古代和元古代洋壳的稀有样品，可能蕴藏着仍有待充分开发的古地球动力学各方面的宝贵信息。在为识别与其复杂的多阶段演化有关的原生和次生成分特征奠定基础的基础上，本研究的目的是：（1）利用大量的常量和微量元素，辅以放射性同位素和稳定同位素以及Fe ~（3+）/Fe ~（2+）分析，探讨不同构造背景和不同构造背景下大型地幔榴辉岩套的多样性成因;（2）使用最少分化和修改的样品提供对古UCOM的化学、氧化和热状态的新约束，这强烈地影响地球动力学和化学循环;（3）从成分和年代学的角度测试地幔榴辉岩的熔融损失与区域CC形成之间的联系。来自科罗拉多高原的榴辉岩捕虏体是作为法拉隆板块的一部分俯冲的、经过充分研究的现代洋底的一部分，代表了古代榴辉岩的独特的现代类似物，对榴辉岩捕虏体的调查将允许确定古代地幔榴辉岩能够可靠地探测UCOM。