Melting of Al‐Rich Phase D up to the Uppermost Lower Mantle and Transportation of H2O to the Deep Earth
Melting of Al‐Rich Phase D up to the Uppermost Lower Mantle and Transportation of H2O to the Deep Earth
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DOI：
10.1029/2019gc008476
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发表时间：
2019-09
期刊：
影响因子：
3.7
通讯作者：
Chaowen Xu;T. Inoue
中科院分区：
文献类型：
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作者：
Chaowen Xu;T. Inoue
我们研究了富铝致密水合硅酸镁D相（PhD）在MgO - Al2O3 - SiO2 - H2O体系中的稳定性，温度范围为14 ~ 25 GPa，温度为900 ~ 1500℃。富Al - PhD具有非常宽的稳定区域，从900°C和14 GPa到至少1,500°C和25 GPa，随着压力的增加表现出很强的温度稳定性。富Al - PhD在地幔过渡带压力下分解为蛋相，而在上、下地幔压力下随着温度升高分解为δ - AlOOH相。富Al - PhD的X射线衍射和拉曼光谱测量结果表明，其单位胞体积略大，但拉曼光谱与无Al - PhD相似。含Al - PhD的宽稳定区是地幔过渡带中水的重要储存场所，表明在正常地幔地热P - T条件下，它可以沿热俯冲向下地幔输送一定量的水。此外，含铝PhD的脱水可能是一系列从过渡带到上下地幔观测到的地震不连续的原因，甚至是一些典型地区的深部地震。
We investigated the stability of the Al‐rich dense hydrous magnesium silicate Phase D (PhD) in a MgO‐Al2O3‐SiO2‐H2O system between 14 and 25 GPa at 900–1,500 °C. Al‐rich PhD has a very wide stability region from 900 °C and 14 GPa to at least 1,500 °C and 25 GPa, showing strong temperature stability with increasing pressure. Al‐rich PhD decomposes to Phase Egg at pressure of the mantle transition zone, whereas it decomposes to δ‐AlOOH phase with a temperature increase at pressure of the uppermost lower mantle. X‐ray diffraction and Raman spectroscopy measurements of Al‐rich PhD show that the unit‐cell volume is slightly larger, but the Raman spectra resemble that of Al‐free PhD. The wide stability region of Al‐bearing PhD would contribute an important storage site for water in the mantle transition zone, suggesting that it can deliver a certain amount of water into the lower mantle along hot subduction and even at the normal mantle geothermal P‐T condition. Furthermore, the dehydration of Al‐bearing PhD might be responsible for a series of observed seismic discontinuities from the transition zone to the uppermost lower mantle and even for deep earthquakes in some typical locations.