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Alumina solubility in orthopyroxene coexisting with sapphirine and quartz

机译:氧化铝与蓝宝石和石英共存于邻二甲苯中的溶解度

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The solubility of alumina in orthopyroxene coexisting with sapphirine and quartz was determined over the P–T interval 1,250–1,350 °C and 10–16 kbar in the system MgO–Al2O3–SiO2. Five isobaric experiments were reversed at 12 kbar at 25 °C intervals between 1,250 and 1,350 °C, and two isothermal experiments at 1,325 °C at 14 and 16 kbar. These constrain the P–T–X relationships of the reaction: ${rm Mg - Tschermak's};{rm orthopyroxene = Mg - sapphirine}_{{rm 221}} ;{rm + quartz}$ . The reaction is strongly temperature dependent and slightly pressure dependent (dP/dT=ca. 94 b K–1) and alumina in orthopyroxene increases by ca. 1 wt% per 26 °C over the temperature interval studied. No corresponding compositional trend in sapphirine was resolvable, an effect attributed to only small changes in alumina solubility with temperature and sluggish kinetics of sapphirine. Entropy calculations for sapphirine based on a recent dataset and minimum constraints from an oxide sum approach fall within the 90% confidence limits of our data, but above a linear-best fit of our data. The latter discrepancy suggests that disequilibrium in sapphirine and/or configurational disorder in orthopyroxene may have been important in the experiments. When taken into account these factors bring our data into reasonable agreement with an oxide sum calculation.
机译:在MgO–Al2 O3 -SiO2 系统中,在P–T区间1,250–1,350°C和10–16 kbar的条件下确定了氧化铝与蓝宝石和石英共存时的溶解度。 。在1250 kB和1,350°C之间以25°C的间隔在12 kbar下进行了五个等压实验,在14 kk和16 kbar的1325°C下进行了两个等温实验。这些约束了反应的P–T–X关系:$ {rm Mg-Tschermak's ;; {rm orthopyroxene = Mg-sapphirine} _ {{rm 221}}; {rm +石英} $。该反应强烈地依赖于温度,而轻微地依赖于压力(dP / dT = ca。94 b K–1 ),邻苯二茂中的氧化铝增加约。在研究的温度范围内,每26°C为1 wt%。蓝宝石中没有相应的组成趋势可以解决,这种作用仅归因于氧化铝溶解度随温度的变化以及蓝宝石动力学缓慢而产生的微小变化。基于最近的数据集和基于氧化物总和方法的最小约束条件下的蓝宝石的熵计算落入我们数据的90%置信范围内,但高于我们数据的线性最佳拟合。后者的差异表明,在实验中,蓝宝石的不平衡和/或邻苯二酚的构型异常可能很重要。考虑到这些因素后,我们的数据与氧化物总和计算就可以合理地吻合。

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    《Contributions to Mineralogy and Petrology》 |2003年第4期|473-483|共11页
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    Department of Geology and Geophysics University of Edinburgh West Mains Rd Edinburgh EH9 3JW UK;

    Department of Geology and Geophysics University of Edinburgh West Mains Rd Edinburgh EH9 3JW UK;

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