Thermodynamic modelling of sodic pyroxene solid-solution and its application in a garnet-omphacite-kyanite-coesite geothermobarometer for UHP metamorphic rocks
Thermodynamic modelling of sodic pyroxene solid-solution and its application in a garnet-omphacite-kyanite-coesite geothermobarometer for UHP metamorphic rocks
复制标题
钠辉石固溶体的热力学模拟及其在超高压变质岩石榴石-绿辉石-蓝晶石-柯石英地温气压计中的应用
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发表时间：
1997
期刊：
影响因子：
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通讯作者：
S. Banno
中科院分区：
文献类型：
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作者：
D. Nakamura;S. Banno
摘要建立了石榴石-绿辉石-蓝晶石-柯石英地质温压计，用于估算超高压榴辉岩的峰期变质压力。为此，我们使用了石榴石的四元正则溶液模型，并提出了钠基辉石的新模型，该模型假定(Na，Ca)M2(Al，Fe3+，Fe2+，Mg)M1Si2O6为双位固溶体，其中M2-和M1-位中的阳离子随机混合，但存在位置间相互作用，不仅在最近的相邻阳离子之间，而且在次最近的相邻阳离子之间。在新的模型中，从以前的实验数据和临界温度定量地推导出总体超额相互作用参数，翡翠组分的活度与朗道理论的活度符合得很好。此外，计算的有序参数与温度和组成的关系与其他实验结果一致。这些事实支持了新模式的实用性。对蓝晶石榴辉岩的地质温压计测定结果表明，西阿尔卑斯山多拉迈拉地块和中国东部苏鲁地区容城的变质条件分别为3.4GPa800 C和3.4GPa800∘C左右。
Abstract A garnet-omphacite-kyanite-coesite geothermobarometer is constructed to estimate the peak metamorphic pressure of ultrahigh-pressure (UHP) eclogites. For this we use a quaternary regular solution model for garnet, and propose a new model for sodic pyroxene that assumes double site solid-solution (Na,Ca)M2(Al,Fe3+,Fe2+,Mg)M1Si2O6, where cations in the M2- and the M1-sites mix randomly but with inter-site interactions, not only between nearest neighboring cations but also between next nearest neighboring cations. In the new model, overall excess interaction parameters are quantitatively deduced from the previous experimental data and critical temperature, and the activity of the jadeite component agrees reasonably with that based on the Landau theory. Furthermore, the relations of the calculated order parameter to temperature and composition are consistent with other experimental works. These facts support the usefulness of the new model. Application of our geothermobarometer to kyanite eclogite gave metamorphic conditions around 3.4 GPa and 800 ∘C for both samples from the Dora Maira Massif, Western Alps, and from Rongcheng County, in the Su-Lu region of eastern China.