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Physics and chemistry of melt transportation in the melt-rock reaction system of the upper mantle

上地幔熔岩反应体系中熔体输送的物理与化学

基本信息

批准号：
14204050
负责人：
OZAWA Kazuhito
金额：
$ 35.03万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

项目摘要

The importance of fluid influx and melt segregation in a melting region in the upper mantle, which may govern abundance and chemical composition of magmas, has been pointed out for many years. In this study, we have transported silicate melt through a partially molten material at high temperature and pressure conditions in laboratory and analyzed physical processes during the melt transportation. We used a few millimeter-sized forsterite-jadeite melt system as an analogue material of natural partially molten mantle peridotites. A jadeite glass-forsterite chip, which had been annealed for a long time at the same P-T conditions to attain textural equilibrium, was put in a graphite capsule with diamond aggregate in one end. The size of diamond is 〜1μm and the thickness is 〜500μm. After the experiments, we examined abundance of melt segregated into the diamond aggregate and texture of melt-segregated region. We focused on the effects of melt fraction (10 vs. 5 %), size of forsterite grain (〜50μm vs.10μm), size distribution of forsterite (untreated vs.sieved to obtain homogeneous size). The results shows that the permeability estimated from the grain size and melt fraction predict too large effect to explain the amount of melt segregated into the diamond aggregate. The size distribution of forsterite is considered to have played an important role to quickly seal the path of melt segregation into the diamond. The examination of forsterite texture by an SEM-EBSD system shows that the sample with wide size distribution shows marked shape and lattice preferred orientation compared to that with narrow size variation. This is consistent with the inference that effective rotation and dislocation creep of is the major mechanism to suppress melt segregation in the partially molten system.

上地幔熔融区的流体流入和熔体分凝作用的重要性，可能决定岩浆的丰度和化学成分，已被指出多年。在本研究中，我们在实验室高温高压条件下将硅酸盐熔体输送通过部分熔融材料，并分析了熔体输送过程中的物理过程。我们用几毫米大小的镁橄榄石-硬玉熔体体系作为天然地幔橄榄岩部分熔融的模拟材料。将在相同的P-T条件下长时间退火达到织构平衡的翡翠玻璃-镁橄榄石切片置于一端装有金刚石骨料的石墨胶囊中。金刚石的尺寸为0.1 μm，厚度为0.500 μm。实验结束后，我们检测了熔凝区的织构和熔凝区的金刚石聚集体中熔凝的丰度。我们着重研究了熔体分数（10%对5%）、镁橄榄石颗粒尺寸（10 μm对10 μm）、镁橄榄石粒度分布（未处理与筛分以获得均匀粒度）的影响。结果表明，从晶粒尺寸和熔体分数估计的渗透率预测太大的效果，以解释量的熔体偏析到金刚石聚集体。镁橄榄石的粒度分布被认为对快速封闭熔体偏析进入金刚石的路径起了重要作用。利用SEM-EBSD系统对镁橄榄石织构的研究表明，与尺寸分布较窄的样品相比，尺寸分布较宽的样品显示出明显的形状和晶格择优取向。这与有效旋转和位错蠕变是抑制部分熔融体系熔体偏析的主要机制的推论是一致的。