Collaborative Research: Experimental Investigation of the Effects of Lithology and Melt Composition on Permeability and 3-D Melt Distribution in Partially Molten Rocks

在洋脊之下，岩石圈板块的分裂使热地幔橄榄岩上升并引起部分熔融。由这一过程形成的浮力熔体通过地幔上升，向洋脊轴集中，形成新的海洋地壳。由于上地幔和下地壳的化学和物理性质受到存在的熔融量的强烈影响，因此更好地了解部分熔融岩石的渗透率至关重要。该项目的目标是对深度部分熔融区域内的熔体迁移和熔体提取速率进行更好的限制。该方法结合了最先进的显微断层扫描技术、FIB/SEM CrossBeam成像技术、高温高压实验室实验和数值模型，将用于量化部分熔融地幔橄榄岩的三维（3-D）熔融分布。以实验确定的三维熔体分布为输入数据，确定不同成分和熔体分数的部分熔融岩石的渗透率。将推导出渗透率、熔体分数和辉石含量之间的经验关系。应力驱动熔体带剪切试样的渗透率各向异性也将计算。这项研究将产生迄今为止关于部分熔融岩石的熔体分布和渗透率的最可靠的结果。这些结果将有助于更好地理解大洋中脊的地球化学和地球物理过程。

Beneath ocean ridges, the divergence of lithospheric plates causes hot mantle peridotite to ascend and induces partial melting. The buoyant melt formed by this process rises through the mantle, is focused towards the ridge axis, and forms new oceanic crust. Because the chemical and physical properties of the upper mantle and lower crust are strongly influenced by the amount of melt present, better understanding of permeability of partially molten rocks is crucial. The goal of this project is to place better constraints on rates of melt migration and melt extraction within the partially molten regions at depth. An approach that integrates state-of-the-art micro-tomography, FIB/SEM CrossBeam imaging techniques, high temperature and pressure laboratory experiments, and numerical models will be used to quantify three-dimensional (3-D) melt distribution in partially molten mantle peridotite. With the experimentally determined 3-D melt distributions as input data, permeability of partially molten rocks with different compositions and melt fractions will be determined. Empirical relations between permeability, melt fraction, and pyroxene content will be derived. Permeability anisotropy for sheared samples with stress-driven melt bands will also be calculated. This study will produce the most reliable results to date on melt distribution and permeability of partially molten rocks. These results will lead to a better understanding of the geochemical and geophysical processes at mid-ocean ridges.