非理想热力学混合作用对固溶体矿物热容的影响——以斜方顽火辉石-正铁辉石固溶体为例

INFLUENCE OF NON-IDEAL THERMODYNAMIC MIXING ON THE HEAT CAPACITIES OF SOLID SOLUTION MINERALS AS EXEMPLIFIED BY ORTHOENSTATITE-ORTHOFERROSILITE SOLUTION

斜方顽火辉石-正铁辉石(MgSiO_3-FeSiO_3)中Fe^(2+)及Mg^(2+)在M_1和M_2两种非等效位置上进行非理想混合。研究表明,辉石的等压热容(C_p)强烈依赖于组成,呈非线性关系,可表示为: 低温时热容的非理想混合效应显著,随着温度的升高,等温热容曲线(空间热容曲面)从一个极大值点(峰脊)分解为两个极大值点(峰脊),且逐渐趋向于理想混合热容直线(或平面)。

Non-ideal thermodynamic mixing of Fe^(2+) and Mg^(2+) in orthoenstatite-orthoferrosillte is thought to take place in two non-equal sites M_1 and M_2, This paper shows that the isobaric heat capacity of orthopyroxene strongly depends on the partitioning between Fe^(2+) and Mg^(2+) and the bulk composition of the solid solution which can be expressed as a non-linear equation.The effects of non-ideal mixing on heat capacity would become rather more evident at lower temperatures, and the isothermal heat capacity curves (or curved surface) in Cp-X diagram would split into those with two extrema (or peak ridges in space) from those with only one extremum(one peak ridge in space) and show a trend toward the heat capacity straight line (or plane in space) for the ideal mixing as the temperature increases.