Experimental determination of the equilibria: rutile + magnesite = geikielite + CO2 and zircon + 2 magnesite = baddeleyite + forsterite + 2 CO2
Experimental determination of the equilibria: rutile + magnesite = geikielite + CO2 and zircon + 2 magnesite = baddeleyite + forsterite + 2 CO2
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DOI：
10.2138/am-2002-1009
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发表时间：
2002-10
影响因子：
3.1
通讯作者：
J. Ferry;R. C. Newton;C. Manning
中科院分区：
文献类型：
--
作者：
J. Ferry;R. C. Newton;C. Manning
通过活塞-气缸装置的反转实验，精确地确定了两种平衡的P-T条件。在8个实验的基础上，金红石-菱镁矿-镁橄榄石平衡的支架在800℃时为7.0-7.1kbar，在850℃时为8.6-8.7kbar，在900℃时为10.5-10.7kbar。在9个实验的基础上，锆石-菱镁矿-斜石英-镁橄榄岩平衡的支架在800℃时为7.1-7.7kbar，在850℃时为9.2-9.4kbar，在900℃时为10.7-10.9kbar。从伯曼以及荷兰和鲍威尔数据库计算的平衡曲线都经过了所有的括号。在1bar和298K下，由实验得到的与Berman数据库一致的吉布斯自由能分别为-1481.94±0.67kJ和-1917.54±1.25kJ。与Holland和Powell数据库的对应值分别为-1479.30±0.74kJ和-1918.47±1.49kJ。这两个平衡的应用表明：(1)苏格兰巴拉丘利什地区硅质白云岩接触变质过程中，硅白云岩接触变质时，流体中CO2的摩尔分数为0.54-1.00；(2)含镁生态岩的超高压变质过程中，CO2的活度可能低至2.10~(-5)；(3)在一次地幔交代过程中，CO2的活度为<；
Abstract The P-T conditions of both equilibria were determined precisely by reversal experiments in a piston-cylinder apparatus. On the basis of 8 experiments, brackets for the rutile-magnesite-geikielite equilibrium are 7.0-7.1 kbar at 800 °C, 8.6-8.7 kbar at 850 °C, and 10.5-10.7 kbar at 900 °C. On the basis of 9 experiments, brackets for the zircon-magnesite-baddeleyite-forsterite equilibrium are 7.1- 7.7 kbar at 800 °C, 9.2-9.4 kbar at 850 °C, and 10.7-10.9 kbar at 900 °C. Considering experimental uncertainties in P (±300 bars) and T (±3 °C), equilibrium curves calculated from both the Berman and the Holland and Powell databases pass through all brackets. Molar Gibbs free energy of formation from the elements at 1 bar and 298 K for geikielite and zircon, derived from the experiments and consistent with the Berman database, are -1481.94 ± 0.67 kJ and -1917.54 ± 1.25 kJ, respectively. Corresponding values consistent with the Holland and Powell database are -1479.30 ± 0.74 kJ and -1918.47 ± 1.49 kJ. Application of the two equilibria indicate that: (1) the mole fraction of CO2 in fluid was 0.54-1.00 when geikielite and baddeleyite formed during contact metamorphism of siliceous dolomites in the Ballachulish aureole, Scotland; (2) the activity of CO2 could have been as low as 2.10-5 during ultra-high pressure metamorphism of magnesite-bearing ecologites; and (3) the activity of CO2 was <0.18 during one instance of mantle metasomatism.