Complementary insights from orogenic and xenolithic eclogites as recorders of mass transfer in subduction zones: A unique case study from the Farallon plate

造山带和捕猎榴辉岩作为俯冲带物质传递记录者的补充见解：来自法拉隆板块的独特案例研究

• 批准号: 467699541
• 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
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/467699541?language=en
• 关键词: Complementary; insights; orogenic; xenolithic; eclogites

Oceanic subduction zones arguably constitute the single most important interface on Earth where significant crust-mantle interaction, with transfer of volatiles and other elements, occurs - processes that are fundamental to planetary evolution. Some mass transfer is mediated by fluids and melts as a function of composition, pressure, temperature and oxygen fugacity. The effects of these parameters on element mobility in this complex environment remain fuzzy, also owing to the incomplete geological record available for any single subduction zone. Due to a unique geological happenstance, the oceanic crust of the Cretaceous Farallon plate has been sampled over an exceptionally large pressure interval (~2.0-4.7 GPa), by tectonically exhumed eclogites in the Franciscan Complex (western United States), and by eclogite xenoliths occurring in the Navajo Volcanic Field, 700 km to the east. Using a representative sample suite, this study aims to fingerprint the sources of the fluids that interacted with the eclogites during deep mass transfer processes in the Farallon plate with bulk-rock Li-B-Mg-Fe isotopes, and detect short-lived fluid flow events with in situ Li-Mg-Fe isotopes. A pressure-temperature-time-oxygen fugacity path will be delineated by combining geothermo-oxybarometry with a novel garnet U-Pb dating tool. Coupled bulk carbon and sulphur concentrations, speciations and isotopic compositions, enhanced by sulphide δ34S, garnet Fe3+/ΣFe and garnet δ56Fe, will be used to assess the interplay between the redox-sensitive elements Fe, C and S, and identify the reactions by which they are mobilised or retained in the slab. Combined, these data will allow to trace the physicochemical controls on mass transfer processes and volatile cycling from forearc to subarc depth, in a single slab, with unprecedented detail.

大洋俯冲带可以说构成了地球上最重要的一个界面，在那里发生了重要的壳幔相互作用，挥发物和其他元素的转移--这是行星演化的基本过程。一些传质是由流体和熔体作为组成、压力、温度和氧逸度的函数来介导的。这些参数在这个复杂的环境中对元素流动性的影响仍然模糊不清，这也是因为任何单一俯冲带的地质记录都不完整。由于一个独特的地质事件，白垩纪法拉隆板块的洋壳已被采样超过一个非常大的压力区间（~2.0-4.7 GPa），构造折返榴辉岩在弗朗西斯杂岩（美国西部），和榴辉岩捕虏体发生在纳瓦霍火山场，700公里以东。使用一个有代表性的样品套件，本研究的目的是指纹的流体与榴辉岩相互作用的过程中，在法拉隆板与块体岩石锂-硼-镁-铁同位素的深部质量转移过程中的来源，并检测短寿命的流体流动事件与原位锂-镁-铁同位素。将地热氧压法与新型石榴石U-Pb定年仪相结合，勾画出压力-温度-时间-氧逸度路径。通过硫化物δ 34 S、石榴石Fe 3 +/Fe 3 + Fe和石榴石δ 56 Fe增强的耦合体碳和硫浓度、形态和同位素组成，将用于评估氧化还原敏感元素Fe、C和S之间的相互作用，并确定它们在板中被动员或保留的反应。结合起来，这些数据将允许跟踪物理化学控制的传质过程和挥发性循环从弧前到弧下深度，在一个单一的板，前所未有的细节。