Al partitioning between phase D and bridgmanite at the uppermost lower mantle pressure
Al partitioning between phase D and bridgmanite at the uppermost lower mantle pressure
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DOI：
10.1007/s00269-021-01163-5
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发表时间：
2021-09
影响因子：
1.4
通讯作者：
Chaowen Xu;S. Kakizawa;S. Gréaux;T. Inoue;Ying Li;Jing Gao
中科院分区：
文献类型：
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作者：
Chaowen Xu;S. Kakizawa;S. Gréaux;T. Inoue;Ying Li;Jing Gao
D相是下地幔上部最重要的含水相，与下地幔中最丰富的矿物、al2o3的主要寄主bridgonite （Brg）共存。Al在D相中的浓度会显著增加D相的热稳定场，因此，Al在Brg和D相之间的分配对于约束深部地幔中的水分布具有特别重要的意义。在此，我们在MgO-Al2O3-SiO2-H2O体系中进行了high - t实验，研究了Al在32 GPa和1350℃下在Brg和D相之间的分配。结果表明，相对于Brg， Al向D相分布较强，分配系数随温度的升高略有降低。含al相D表现出很高的热稳定区，但在28gpa和1350℃左右完全分解，此时Brg与大量熔体共存。因此，建议850 km （28gpa）深度为含水矿物的第二大瓶颈。这可能为俯冲带的几个重要地球物理观测提供新的线索。
Phase D is proposed to be the most important hydrous phase at the upper part of the lower mantle, and it has been shown to coexist with bridgmanite (Brg), the most abundant mineral and main host for Al2O3in the lower mantle. The concentration of Al in Phase D could significantly increase the thermal stability field of Phase D, therefore, partitioning of Al between Brg and Phase D is of particular importance to constrain water distribution in the deep mantle. Here, we performed highP–Texperiments in MgO–Al2O3–SiO2–H2O system to investigate the partitioning of Al between Brg and Phase D up to 32 GPa and 1350 °C. Our results indicated that Al distributes strongly into Phase D relative to Brg and the partition coefficient slightly decreases with increasing temperature. Al-bearing Phase D exhibits a very high thermal stability region, but it completely decomposed around 28 GPa and 1350 °C, at which point Brg coexisted with a large amount of melt. The depth ~ 850 km (28 GPa) is thus proposed to be the second choke point for hydrous minerals. This may shed new lights on several important geophysical observations in subduction zones.