EAGER: Collaborative Research: Continental Subduction and Deep Crustal Melting

对于许多地壳岩性来说，俯冲的大陆地壳可以达到高于固相的压力-温度条件，但深层地壳融化的条件、时间和后果在很大程度上尚未被探索。虽然已经有超高压（UHP）熔融的实验研究，但很少有基于自然实例的现场研究；现有的工作主要集中在与超高压地形相关的花岗岩体的年龄和化学特征上，而不是通常含有超高压岩石的混杂岩。在俯冲过程中，大量部分熔融地壳的产生对地幔到地壳的质量和热量传递、部分熔融物质在深部产生的造山作用以及造山景观的演化（如高原的发育）都有影响。此外，在了解(U)HP岩石在挖掘和随后的造山过程中叠印的机制时，必须考虑部分熔融地壳的作用。这项探索性研究（EAGER）项目旨在从与榴辉岩空间相关的岩浆体（白色体、伟晶岩）中获取U/Pb锆石，以确定锆石是否在超高压条件下结晶并因此熔化。如果这项探索性研究取得成功，它将为一个更大规模的项目奠定基础，其最终目标是验证一个假设，即在一些造山带，大陆地壳的部分熔融发生在大陆俯冲期间，并与造山带的热力学演化和超高压岩石的发掘有动态联系。对足够样品材料的追求将在西片麻岩区（挪威）进行，因为它是一个可接近的地点，有大量暴露于混杂岩中的超高压岩石；有些榴辉岩体本身是混合质的。

Subducted continental crust can attain pressure-temperature conditions that are above the solidus for many crustal lithologies, but the conditions, timing, and consequences of deep crustal melting are largely unexplored. Although there have been experimental investigations of ultrahigh-pressure (UHP) melting, there are very few field-based studies of natural examples; existing work has focused largely on the age and chemical characteristics of granitoid bodies that are associated with UHP terrains and not on migmatites that commonly host UHP rocks. The generation of large amounts of partially molten crust during subduction has implications for mass and heat transfer from the mantle to the crust, orogenic growth by the addition of partially molten material generated at depth, and evolution of orogenic landscapes (e.g. development of plateaux). Moreover, the role of partially molten crust must be considered in understanding the mechanisms by which (U)HP rocks are overprinted during exhumation and subsequent orogenic processes. This proposed Early Grant for Exploratory Research (EAGER) project is designed to obtain U/Pb zircon ages from magma bodies (leucosomes, pegmatites) spatially associated with eclogite to determine if zircon crystallized and thus melting occurred at UHP conditions. If this exploratory study is successful, it will set up the background canvas for a larger scale project with the ultimate goal of testing the hypothesis that, in some orogens, partial melting of continental crust occurs during continental subduction and is dynamically linked to the thermal-mechanical evolution of orogens and the exhumation of UHP rocks. The pursuit for adequate sample material will take place in the Western Gneiss Region (Norway) because it is an accessible locale with abundant exposure of UHP rocks that are hosted by migmatite; some eclogite bodies are themselves migmatitic.