Stability of dense hydrous magnesium silicate phases in the systems Mg2SiO4-H2O and MgSiO3-H2O at pressures up to 27 GPa
Stability of dense hydrous magnesium silicate phases in the systems Mg2SiO4-H2O and MgSiO3-H2O at pressures up to 27 GPa
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DOI：
10.1007/s002690000097
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发表时间：
2000-09
影响因子：
1.4
通讯作者：
E. Ohtani;H. Mizobata;H. Yurimoto
中科院分区：
文献类型：
--
作者：
E. Ohtani;H. Mizobata;H. Yurimoto
在20 ~ 27 GPa下，对MgSiO 3和15wt%H_2O以及Mg_2SiO_4和5wt%H_2O以及11wt%H_2O体系进行了高压相平衡实验。根据这些体系中的相关系，结合前人对相关体系的研究工作，阐明了MgO-SiO_2-H_2 O体系中致密含水镁硅酸盐在10 ~ 27 GPa压力范围内的稳定性关系。结果表明，随着含水量的增加，G相的稳定性场扩大，与D相和F相的稳定性场相同。储存在下降的冷板中的蛇纹石中的水被输送到大于200 km的深度，在那里蛇纹石分解成A相、顽火辉石和流体的混合物。在较高压力下出现的含水相的反应顺序随含水量而变化。在含水量小于约2wt%的板中，相A将水运送到450 km的深度。450 ~ 660 km过渡带的主要水储层为含水的瓦氏岩、含水的林伍德岩和钛铁矿。超水相B是下地幔最上部670 ~ 800 km的水储集层，而G相只出现在800 km以上的深度。在局部水富集大于2重量%的冷板中，随着深度的增加出现以下含水相：A相至450 km，A相和G相从450 km至550 km，水镁石、超含水相B和G相从550 km至800 km，G相在深度大于800 km。
We conducted high-pressure phase equilibrium experiments in the systems MgSiO3with 15 wt% H2O and Mg2SiO4with 5 wt% and 11 wt% H2O at 20 ∼ 27 GPa. Based on the phase relations in these systems, together with the previous works on the related systems, we have clarified the stability relations of dense hydrous magnesium silicates in the system MgO-SiO2-H2O in the pressure range from 10 to 27 GPa. The results show that the stability field of phase G, which is identical to phase D and phase F, expands with increasing water contents. Water stored in serpentine in the descending cold slabs is transported into depths greater than 200 km, where serpentine decomposes to a mixture of phase A, enstatite, and fluid. Reaction sequences of the hydrous phases which appear at higher pressures vary with water content. In the slabs with a water content less than about 2 wt%, phase A carries water to a depth of 450 km. Hydrous wadsleyite, hydrous ringwoodite, and ilmenite are the main water reservoirs in the transition zone from 450 to 660 km. Superhydrous phase B is the water reservoir in the uppermost part of the lower mantle from 670 to 800 km, whereas phase G appears in the lower mantle only at depths greater than 800 km. In cold slabs with local water enrichment greater than 2 wt%, the following hydrous phases appear with increasing depths; phase A to 450 km, phase A and phase G from 450 km to 550 km, brucite, superhydrous phase B, and phase G from 550 km to 800 km, and phase G at depths greater than 800 km.