Petrology of low-grade high-pressure metapelites from the External Hellenides (Crete, Peloponnese); a case study with attention to sodic minerals
Petrology of low-grade high-pressure metapelites from the External Hellenides (Crete, Peloponnese); a case study with attention to sodic minerals
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DOI：
10.1127/ejm/3/2/0343
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发表时间：
1991-04
影响因子：
2.1
通讯作者：
T. Theye;E. Seidel
中科院分区：
文献类型：
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作者：
T. Theye;E. Seidel
在外部希腊尼德的千枚石-石英岩单元中，等值岩石矿物组成的区域差异表明，变质作用的PT条件是从E-克里特经W-克里特到伯罗奔尼特的分级。在克里特岛东部和中部的变质沉积中，钠长石矿物以相当单一的组合出现，即钠长石-I-绿泥石和副石+绿泥石。该地区的P和T约为300-350℃，8-10kbar，以具石榴石、拟绿泥石或苏铁榴石的共生体为基础。通过W-Crete(400±50℃，10±3kbar，利用类绿泥石-碳磷石组合)，在广泛分布的类绿泥片岩中仍然存在副铜矿+绿泥石，在含副铜矿的变质岩中已观察到蓝色角闪石(假名)。在伯罗奔尼撒半岛观察到的矿物副矿物种类较多，绿泥质片岩中的绿泥石+副矿物和蓝闪石片岩中的蓝色角闪石+副矿物普遍存在。也有含绿泥石-蓝闪石的片岩，在某些情况下含有额外的钠基辉石，或局部石榴石。对于伯罗奔尼撒来说，应用Holland&Powell(1990)的热力学数据来约束变质作用的P和T，得到450±30℃和17±4kbar。全岩和矿物分析表明，除了P和T外，成分参数对特定矿物共生的发展也很重要。碳磷岩仅限于镁质岩石，对于中等的镁铁比，绿泥石和蓝闪石、绿泥石和蓝闪石或钠辉石的组合的产状取决于增加Fe3+/Al比，在给定的P和T。确定了前进性变化的反应，变质演化可能与榴辉岩相有关。
In the Phyllite-Quartzite Unit of the External Hellenides regional differences in the mineralogical compositions of equivalent rocks indicate a gradation in PT conditions of metamorphism from E-Crete via W-Crete to the Peloponnese.In metasediments of Eastern and Central Crete, sodic minerals appear in rather monotonous assemblages, ie albite-I-chlorite and paragonite+ chlorite. For this region, the estimated P and T are about 300-350 C, 8-10 kbar, based on parageneses with carpholite, chloritoid or sudoite. Passing to W-Crete (400±50 C, 10±3 kbar, using chloritoid-carpholite assemblages), paragonite+ chlorite is still present in widespread chloritoid schists, and blue amphiboles (as pseudomorphs) have been observed in paragonite-bearing metasediments. A greater variety of mineral parageneses has been observed in the Peloponnese, where chlorite+ paragonite in chloritoid schists and blue amphibole+ paragonite in glaucophane schists are widespread. Paragonite-bearing chloritoid-glaucophane schists also occur, which in some cases contain additional sodic pyroxene, or locally garnet. For the Peloponnese, application of thermodynamic data of Holland & Powell (1990) to constrain P and T of metamorphism yields 450±30 C and 17±4 kbar. Whole-rock and mineral analyses demonstrate the importance of compositional parameters, besides P and T, on the development of a specific mineral paragenesis. Carpholite is restricted to magnesian rocks; for intermediate Mg/Fe2+ ratios, the occurrence of assemblages with either chloritoid or glaucophane, with chloritoid and glaucophane, or with Na-pyroxene, is determined by increasing Fe3+/Al ratio, at given P and T. Garnet occurs in rocks with higher Mn/Fe2+ ratio. Reactions responsible for the prograde changes are identified, and the metamorphic evolution may be connected towards higher grades with the eclogite facies.