Ab initio investigation of high‐pressure phase relation and elasticity in the NaAlSi2O6 system
Ab initio investigation of high‐pressure phase relation and elasticity in the NaAlSi2O6 system
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DOI：
10.1029/2010gl044310
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发表时间：
2010-09
影响因子：
5.2
通讯作者：
K. Kawai;T. Tsuchiya
中科院分区：
文献类型：
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作者：
K. Kawai;T. Tsuchiya
俯冲的地壳含有铝相和不相容的元素，如钠。为了了解俯冲地壳的命运及其如何在地球内循环，研究宿主相的高压稳定性和弹性特性是很重要的。本文采用第一性原理计算方法研究了NaAlSi2O6硬玉、NaAlSiO4铁酸钙（CF）型相和SiO2硬石。在18 GPa左右的温度下，硬玉分解成CF型相和辉石的组合，纵波（18.7%）、横波（26.4%）、体声（13.3%）速度和密度（15.1%）显著增加。这种过渡条件与地幔过渡带中660 km不连续的接近表明，地震观测到的反射分裂可能与这种相变有关，这意味着地壳物质向地幔过渡带俯冲。
Subducted crusts contain aluminous phases with incompatible elements such as sodium. In order to understand the fate of subducted crusts and how they recycle within the Earth, it is important to investigate high‐pressure stability and elastic properties of host phases. Here we have studied NaAlSi2O6 jadeite, a NaAlSiO4 calcium ferrite (CF)‐type phase, and SiO2 stishovite by means of a first principles computation method. Jadeite was found to dissociate into an assemblage of the CF‐type phase and stishovite at about 18 GPa, associated with remarkable increases of compressional wave (18.7%), shear wave (26.4%), bulk sound (13.3%) velocities, and density (15.1%). Proximity of this transition condition to the 660 km discontinuity in the mantle transition zone suggests that seismically observed splitting of the reflection could be related to this phase transition, implying subduction of crustal materials down to the mantle transition zone.