Postspinel transformations in the system Mg2SiO4-Fe2SiO4 Element partitioning, calorimetry, and thermodynamic calculation
Postspinel transformations in the system Mg2SiO4-Fe2SiO4 Element partitioning, calorimetry, and thermodynamic calculation
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Mg2SiO4-Fe2SiO4 体系中的后尖晶石转变 元素分配、量热和热力学计算
DOI：
10.1029/gm101p0373
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
E. Ito
中科院分区：
文献类型：
--
作者：
M. Akaogi;H. Kojitani;K. Matsuzaka;Toshihiro Suzuki;E. Ito
在1873 K、18.5 GPa和20.4 GPa条件下，实验测定了mg2sio4 - fe2sio4体系中尖晶石和镁辉石共存的组成，以约束相对富fe2sio4成分中尖晶石后转变的平衡边界。在可控气氛下，用微分滴液法测定了m2sio3 - fe2sio3体系中辉石和钙钛矿固溶体的量热。利用上述数据和已发表的MgO-FeO-SiO - 2体系高压相热力学数据，对尖晶石后相变的相关系进行了热力学计算。计算的边界与Ito和Takahashi的实验基本一致。计算得出尖晶石向钙钛矿+镁武铁矿转变的过渡区间为0.01 ~ 0.18 GPa。与之前的热力学计算结果相反，随着温度的升高，钙钛矿-镁钨矿场扩展到富含fe2sio4的一侧。目前的热力学数据表明，在尖晶石场和钙钛矿+镁云母场之间的富mg2sio4 - fe2sio4体系中，镁云母-镁云母组合在相对较低的温度下具有稳定性。
Compositions of coexisting spinel and magnesiowustite in the system Mg 2 SiO 4 -Fe 2 SiO 4 have been experimentally determined at 18.5 and 20.4 GPa at 1873 K to constrain equilibrium boundaries of the postspinel transitions in relatively Fe 2 SiO 4 -rich composition. Calorimetric measurements of pyroxene and perovskite solid solutions in the system Mg 2 SiO 3 -Fe 2 SiO 3 have been performed by a differential drop-solution method in a controlled atmosphere. Using the above data with published thermodynamic data on the high-pressure phases in the system MgO-FeO-SiO 2 , phase relations of the postspinel transitions have been thermodynamically calculated. The calculated boundaries are generally consistent with the experiments by Ito and Takahashi. The calculated transition interval of spinel to perovskite + magnesiowustite is about 0.01-0.18 GPa for mantel spinel composition. The perovskite-magnesiowustite field expands to the Fe 2 SiO 4 -rich side with increasing temperature, in contrast to previous thermodynamic calculations. The present thermodynamic data show stability of an assemblage of magnesiowustite-stishovite in the Mg 2 SiO 4 -rich composition of the Mg 2 SiO 4 -Fe 2 SiO 4 system between the fields of spinel and of perovskite + magnesiowustite at relatively low temperatures.