The effect of TiO2 and Fe2O3 on metapelitic assemblages at greenschist and amphibolite facies conditions: mineral equilibria calculations in the system K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3
The effect of TiO2 and Fe2O3 on metapelitic assemblages at greenschist and amphibolite facies conditions: mineral equilibria calculations in the system K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3
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DOI：
10.1046/j.1525-1314.2000.00269.x
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发表时间：
2000-09
影响因子：
3.4
通讯作者：
White;Powell;Holland;Worley
中科院分区：
文献类型：
--
作者：
White;Powell;Holland;Worley
采用Thermocalc和内部一致的热力学数据，对K2 O-FeO-MgO-Al 2 O3-SiO2-H2O-TiO 2-Fe 2 O3（KFMASHTO）体系的矿物平衡进行了计算，结果表明TiO 2和Fe 2 O3对绿片岩相和角闪岩相矿物平衡的影响是有限的。黑云母和绿帘石的端元数据和活性-成分关系（用天然岩石数据校准）以及石榴石的活性-成分数据（用实验数据校准）为TiO 2和Fe 2 O 3对这些矿物稳定性的影响提供了新的约束。热力学模型为钛铁矿-赤铁矿和磁铁矿-ulvospinel固溶体占有序-无序在这些阶段允许的分布的TiO 2和Fe 2 O 3之间的氧化物矿物和硅酸盐矿物进行计算。计算结果表明，小到中等量的TiO 2和Fe 2 O 3在典型的变岩块体组合物中的硅酸盐矿物平衡在绿片岩角闪岩相的影响不大，在KFMASH计算的。此外，大量的TiO 2到典型的泥质散装组合物的稳定性的硅酸盐组合的影响不大，相反，岩石丰富的Fe 2 O3开发一个显着不同的变质序列从共同的Barrovian序列。特别是，富Fe 2 O3的变岩显示出十字石和石榴石的稳定性领域的显着减少，以更高的压力，与KFMASH网格预测。
Mineral equilibria calculations in the system K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3 (KFMASHTO) using thermocalc and its internally consistent thermodynamic dataset constrain the effect of TiO2 and Fe2O3 on greenschist and amphibolite facies mineral equilibria in metapelites. The end‐member data and activity–composition relationships for biotite and chloritoid, calibrated with natural rock data, and activity–composition data for garnet, calibrated using experimental data, provide new constraints on the effects of TiO2 and Fe2O3 on the stability of these minerals. Thermodynamic models for ilmenite–hematite and magnetite–ulvospinel solid solutions accounting for order–disorder in these phases allow the distribution of TiO2 and Fe2O3 between oxide minerals and silicate minerals to be calculated. The calculations indicate that small to moderate amounts of TiO2 and Fe2O3 in typical metapelitic bulk compositions have little effect on silicate mineral equilibria in metapelites at greenschist to amphibolite facies, compared with those calculated in KFMASH. The addition of large amounts of TiO2 to typical pelitic bulk compositions has little effect on the stability of silicate assemblages; in contrast, rocks rich in Fe2O3 develop a markedly different metamorphic succession from that of common Barrovian sequences. In particular, Fe2O3‐rich metapelites show a marked reduction in the stability fields of staurolite and garnet to higher pressures, in comparison to those predicted by KFMASH grids.