Potential host phase of aluminum and potassium in the Earth’s lower mantle
Potential host phase of aluminum and potassium in the Earth’s lower mantle
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DOI：
10.2138/am-2001-5-614
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发表时间：
2001-05
影响因子：
3.1
通讯作者：
N. Miyajima;T. Yagi;K. Hirose;T. Kondo;K. Fujino;H. Miura
中科院分区：
文献类型：
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作者：
N. Miyajima;T. Yagi;K. Hirose;T. Kondo;K. Fujino;H. Miura
用X射线衍射仪和分析电子显微镜研究了大洋中脊玄武岩在下地幔条件下相变形成的富铝相。该物相具有六方对称性(空间群P63/m)，组成为[(M+，Ca)1(Mg，Fe)2]∑3(Al，Si)5.5-6.0O12，其中M=Na+，K+，与硅酸盐钙钛矿、钙铁氧体结构相共存。无碱固溶体为[Ca0.79Mg0.12]∑0.91[Mg]2.00[Al4.09Si1.48]∑5.57⃞0.43O12，晶胞参数为a=8.765(3)？，c=2.762(3)？，V=0.79(2)？3，Z=1，公式重量=429.31，计算密度分别为3.88g/cm~3和4.16g/cm~3。这一富铝相被认为与最近报道的六方相相同，因此六方相有可能在下地幔中赋存碱和碱土元素。
Abstract An Al-rich phase produced by phase transformation from a natural mid-oceanic ridge basalt under lower mantle conditions was studied by X-ray diffraction and analytical transmission electron microscopy. The phase, coexisting with silicate perovskites, the Ca-ferrite-structure phase, and stishovite, has hexagonal symmetry (space group P63/m) and the composition [(M+,Ca)1(Mg,Fe)2]∑3(Al,Si)5.5-6.0O12, where M = Na+, K+. The alkali-free phase with the complex solid solution, [Ca0.79Mg0.12] ∑ 0.91[Mg]2.00 [Al4.09Si1.48] ∑ 5.57⃞0.43O12, has a unit cell with a = 8.765 (3) Å, c = 2.762 (3) Å, V = 183.7 (2) Å3, Z = 1, a formula weight = 429.31, and a calculated density = 3.88 g/cm3 at 0 GPa and 4.16 g/cm3 at 23 GPa. This Al-rich phase is considered to be same as the hexagonal phases recently reported, and thus the hexagonal phases can potentially host alkali and alkali-earth elements in the lower mantle.