Characteristics and Genesis of Garnet from Loufan District, Shanxi Province
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摘要: 石榴石是山西娄烦吕梁群变质岩系中广泛出现的特征矿物,赋存原岩为泥砂质和富铝的泥质岩类。对石榴石进行了电子探针成分分析及相关计算以阐明其成分与变质温度、压力间的关系。结果表明,石榴石成分的变化有一定的规律性。利用地质温度计估算变质温度和压力,结果表明,随着变质温度和压力的升高,石榴石成分中钙铝榴石、锰铝榴石的摩尔分数降低,而铁铝榴石和镁铝榴石的摩尔分数升高。这种变化规律是由于在不同的压力条件下,石榴石晶体结构中二价阳离子处于八面体配位时离子配位半径的不同引起的。Abstract: Garnets from Loufan district, Shanxi Province, are widely distributed through the layers——Lüliang group metamorphic rocks, which formed from metamorphism of mudstone and sandstone. In order to find out the interrelations between garnet and the metamorphic conditions, EPMA and the mineral assemblage geothermometry are adopted. The results show that from the north to the south of the research area, the amounts of CaO and MnO in garnets decrease, while that of FeO and MgO increase. This regular variation is controlled by the metamorphic conditions, especially the pressure, which can be explained by different cation radiuses in the octahedral coordination site of garnet lattice under different pressure.
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Keywords:
- garnet /
- geothermometry /
- coordination radius /
- genesis /
- Loufan district /
- Shanxi Province
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