Pyroxene Phase Equilibria for Thermobarometry of FeldspathicMafic and Ultramafic Rocks

在CaO-MgO-Al2O3-SiO体系中，温度为925℃~ 1175℃，压力为5000 ~ 7500 bar，测定长辉石+透辉石+长辉石+钙长石组合中辉石的组成。这些实验的结果将与本实验程序先前在常压、2500巴和5000巴下得到的结果相结合。实验数据将用于构建和约束亚固相辉石相平衡的经验和热力学模型，然后可应用于估算felspathic，基性和超基性岩石的平衡温度和压力的方法。在Ca/Mg比和Al含量方面，通过从高值和低值开始的成分接近平衡成分，辉石组成将被逆转。实验将五氧化二钒作为高温溶剂，促进晶粒生长和化学平衡；在这个实验程序的早期发展的几条证据表明，这种技术对所研究的平衡产生的影响可以忽略不计。将通过岩石学、电子显微探针和粉末x射线衍射进行成分和相组合分析，并根据需要辅以扫描和透射电子显微镜和单晶x射线衍射。

Experiments to determine the compositions of pyroxenes in the assemblage enstatite + diopside + forsterite + anorthite will be performed in the systems CaO-MgO-Al2O3-SiO at temperatures from 925oC to 1175oC, and pressures of 5000 and 7500 bars. Results from these experiments will be combined with results obtained earlier in this experimental program at atmospheric pressure, and at 2500 and 5000 bars. The experimental data will be used to construct and to constrain empirical and thermodynamic models of subsolidus pyroxene phase equilibria, which may then be applied to methods of estimating temperatures and pressures of equilibration of felspathic, mafic and ultramafic rocks. Pyroxene compositions will be reversed, both in terms of Ca/Mg ratio and Al contents by approaching the equilibrium compositions from starting compositions with both higher and lower values. Experiments will use vanadium pentoxide as a high-temperature solvent to promote grain growth and chemical equilibration; several lines of evidence developed earlier in this experimental program demonstrate that this technique produces negligible effects upon the equilibria under investigation. Analysis of compositions and phase assemblages will be performed petrographically, by electron microprobe, and powder X-ray diffraction, supplemented by scanning and transmission electron microscopy and single crystal X-ray diffraction as required.