Polymineralic inclusions in eclogite-facies metapelites from Tanzania – insights on partial melting and geodynamic processes in a 2 Ga old subduction zone

高级变质岩中的多矿物包裹体是一个很有前途的工具，以获得新的见解的形成部分熔体的熔体成分，流体制度和地球动力学背景。目前对多矿物包裹体的研究主要集中在深熔壳岩和麻粒岩中，或俯冲陆壳岩石中，而坦桑尼亚Usagaran带榴辉岩相变岩则代表了俯冲洋壳的一部分，为研究洋壳岩石的部分熔融过程提供了难得的机会。在这些变岩中的多矿物包裹体是不同的，因为硅质云母的矿物组合旁边发生的碳的指示CO2占主导地位的COH流体的存在下，熔体和/或流体的不混合作为一个可能的形成过程。此外，该研究区提供了一个难得的机会，调查一个最古老的已知俯冲带（2 Ga）和结果可能揭示在地球的早期历史的地热梯度。拟议的研究将集中在：（1）在最古老的古代俯冲带之一的熔体形成的时间和过程，（2）所产生的熔体的成分和存在的CO2的影响。利用光学显微镜、电子探针、拉曼光谱和LA-ICP-MS等手段对样品进行分析，并利用活塞筒重熔实验对多矿物包裹体进行了再均匀化处理。

Polymineralic inclusions in high-grade metamorphic rocks are a promising tool to obtain new insights on the formation of partial melts with respect to melt composition, fluid regime and geodynamic setting. All studies on polymineralic inclusions reported so far occur either in anatectic crustal rocks and granulites or in rocks from subducted continental crust.By contrast, the eclogite-facies metapelites of the Usagaran belt in Tanzania represent a part of the subducted oceanic crust, providing the rare opportunity to investigate the process of partial melting in oceanic rocks. Polymineralic inclusions in these metapelites are distinct, because siliceous mica-bearing mineral assemblages occur beside carbonaceous ones indicating the presence of a CO2-dominated COH fluid, with unmixing of melt and/or fluid as a possible formation process. Furthermore, the study area provides the exceptional opportunity to investigate one of the oldest known subduction zones (2 Ga) and the results might shed light on the geothermal gradients in the early Earth’s history.The proposed research shall focus on: (1) Timing and process of melt formation in one of the oldest ancient subduction zones, (2) composition of the melts produced and the influence of the presence of CO2. The samples will be analyzed by means of optical microscopy, electron microprobe, Raman spectroscopy and LA-ICP-MS. Furthermore, the polymineralic inclusions will be rehomogenized by remelting experiments with a piston cylinder.