Second critical endpoint in the peridotite‐H2O system
Second critical endpoint in the peridotite‐H2O system
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DOI：
10.1029/2005jb004125
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发表时间：
2007-03
影响因子：
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通讯作者：
K. Mibe;M. Kanzaki;T. Kawamoto;K. Matsukage;Y. Fei;S. Ono
中科院分区：
文献类型：
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作者：
K. Mibe;M. Kanzaki;T. Kawamoto;K. Matsukage;Y. Fei;S. Ono
[1]橄榄岩-H2O系统的第二个临界终点已被确定使用X射线照相技术与Kawai型，双级，多砧系统驱动的DIA型六面顶压机（SPEED-1500）安装在SPring-8，日本。第二临界点的压力是通过改变实验压力时，X线片上圆形的出现和消失来确定的。在高达3.6GPa的实验中，两个流体相（即，含水流体和含水硅酸盐熔体）。然而，在4.0 GPa时，我们无法在射线照相图像中区分这两个阶段。这些观测结果表明橄榄岩-H2O系统的第二个临界终点发生在3.8 GPa和1000°C（对应于110 km的深度）附近。我们的实验结果表明，含水硅酸盐熔体和地球地幔中的含水流体变得无法区分彼此和含水地幔橄榄岩的熔融温度不能再定义超过这个临界条件。第二个临界点的位置可以解释以前观察到的地幔橄榄岩中的水流体在3-4 GPa左右的组成和连通性的急剧变化，并可能在地球内部的岩浆作用和化学演化中发挥重要作用。
[1] The second critical endpoint in the peridotite-H2O system has been determined using an X-ray radiography technique together with a Kawai-type, double-stage, multianvil system driven by DIA-type cubic press (SPEED-1500) installed at SPring-8, Japan. The pressure of the second critical endpoint was determined by the appearance and disappearance of round shape in the radiographic images with changing the experimental pressure. In the experiments up to 3.6 GPa, two fluid phases (i.e., aqueous fluid and hydrous silicate melt) were observed. At 4.0 GPa, however, we could not distinguish these two phases in the radiographic images. These observations indicate the second critical endpoint occurs at around 3.8 GPa and 1000°C (corresponding to a depth of ∼110 km) in the peridotite-H2O system. Our experimental results suggest that hydrous silicate melt and aqueous fluid in the Earth's mantle become indistinguishable from each other and that melting temperature of hydrous mantle peridotite can no longer be defined beyond this critical condition. This position of the second critical endpoint could explain the previously observed drastic changes in composition and connectivity of aqueous fluid in mantle peridotite at around 3–4 GPa and could play an important role in magmatism and chemical evolution of the Earth's interior.