Morphological stability of hydrous liquid droplets at grain boundaries of eclogite minerals in the deep upper mantle
Morphological stability of hydrous liquid droplets at grain boundaries of eclogite minerals in the deep upper mantle
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DOI：
10.2465/jmps.170309
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发表时间：
2017
影响因子：
0.7
通讯作者：
K. Matsukage;Mika Hashimoto;Yu Nishihara
中科院分区：
文献类型：
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作者：
K. Matsukage;Mika Hashimoto;Yu Nishihara
基于二面角的实验约束，研究了俯冲板片玄武岩部分榴辉岩矿物晶界处含水液滴的形态稳定性。我们在 1000 °C 的温度和 4 至 16 GPa 的压力下测量了榴辉岩-H2O 系统中的二面角。含水液体与石榴石-石榴石的二面角 (θGG-L) 随着压力的增加而增加，从 4 GPa 时的 46° 到 12 GPa 时的 66°，尽管在压力高于 12 GPa 时表现出微弱的下降趋势。随着压力的增加，含水液体与单斜辉石-单斜辉石的二面角 (θCC-L) 几乎恒定（在 4 GPa 和 10 GPa 下分别为 61 和 59°）。在 4-10 GPa 压力下，含水液体与石榴石-单斜辉石 (θGC-L) 的二面角 (θGC-L) 为 73-76°，并且始终高于 θGG-L 和 θCC-L。通过应用两固相（石榴石和单斜辉石）体系中液体的形态稳定性准则和三维四配位晶格的键渗流理论，我们发现，在上地幔4~14 GPa的广泛压力条件下，当石榴石的晶粒尺寸与单斜辉石的晶粒尺寸相同时，含水液体在冷板片中榴辉岩矿物的晶粒棱角处被隔离。因此，当板片冷时，含有含水液滴的玄武岩地壳可能将水带到最下部的上地幔和地幔过渡带。
The morphological stability of hydrous liquid droplets at grain boundaries of eclogite minerals in the basaltic part of a subducting slab were investigated based on experimental constraints for the dihedral angles. We measured the dihedral angles in the eclogite–H2O system at a temperature of 1000 °C and at pressures ranging from 4 to 16 GPa. The dihedral angle of hydrous liquid versus garnet–garnet (θGG–L) increased with increasing pressure from 46° at 4 GPa to 66° at 12 GPa, although it showed a weak decreasing trend at pressures higher than 12 GPa. The dihedral angle of hydrous liquid versus clinopyroxene–clinopyroxene (θCC–L) was almost constant with increasing pressure (61 and 59° at 4 and 10 GPa, respectively). The dihedral angle of hydrous liquid versus garnet–clinopyroxene (θGC–L) was 73–76° at 4–10 GPa, and it was always higher than θGG–L and θCC–L. By applying the morphological stability criteria for liquid in a system with two solid phases (garnet and clinopyroxene) and bond percolation theory for a three–dimensional lattice of tetracoordination, we found that the hydrous liquid was isolated at the grain edges and corners of eclogite minerals in the cold slab under a wide range of pressure conditions of the upper mantle from 4–14 GPa when the grain size of garnet was equal to that of clinopyroxene. Thus, basaltic crust containing hydrous liquid droplets may carry water to the lowermost upper mantle and the mantle transition zone when the slab is cold.