Decompression‐induced growth of albite porphyroblasts, Fleur de Lys Supergroup, western Newfoundland
Decompression‐induced growth of albite porphyroblasts, Fleur de Lys Supergroup, western Newfoundland
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减压诱导的钠长石卟啉细胞生长，百合花超群，纽芬兰西部
DOI：
10.1111/j.1525-1314.1991.tb00537.x
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发表时间：
1991
影响因子：
3.4
通讯作者：
A. O'Beirne
中科院分区：
文献类型：
--
作者：
R. Jamieson;A. O'Beirne
摘要在纽芬兰西部的Fleur de Lys超群中，钠长石变斑晶广泛分布于泥质和半泥质片岩中。结构和矿物组合表明，钠长石是在从约500° C，9 kbar的P-T条件到550° C，6.5 kbar的条件的近等温减压过程中生长的。含钠长石片岩的三种成分变体，这里称为PMAQ（钠长石-白云母-钠长石-石英）、MMAQ（微斜长石-白云母-钠长石-石英）和PMMQ（钠长石-白云母-玛格丽特-石英），可以根据前成斑矿物组合来区分。这些组合的共存流体的组合物[log a（Na+/H+）与log a（K+/H+）]的分析表明，随着压力和温度的变化，钠长石的稳定性领域扩大在共存的矩阵层状硅酸盐的费用。这促进了钠长石在先前存在的或新形成的晶核上的生长。PMAQ和PMMQ样品中的晚期奥长石与基质石榴石被斜长石+云母°绿泥石替换有关，特别是在强烈剪切的样品中。
Abstract Albite porphyroblasts are widely distributed in pelitic and semi-pelitic schists of the Fleur de Lys Supergroup, western Newfoundland. Textures and mineral assemblages indicate that albite grew during nearly isothermal decompression from P-T conditions of about 500° C, 9 kbar, to conditions of 550° C, 6.5 kbar. Three compositional varieties of albite-bearing schists, here termed PMAQ (paragonite-muscovite-albite-quartz), MMAQ (microcline-muscovite-albite-quartz), and PMMQ (paragonite-muscovite-margarite-quartz), can be distinguished on the basis of pre-porphyroblast mineral assemblages. Analysis of these assemblages in terms of the composition of the coexisting fluid [log a(Na+/H+) versus log a(K+/H+)] suggests that, as pressure and temperature changed, the stability field of albite expanded at the expense of coexisting matrix phyllosilicates. This promoted growth of albite on pre-existing or newly formed nuclei. Late oligoclase in PMAQ and PMMQ samples is associated with replacement of matrix garnet by plagioclase + mica ° Chlorite, particularly in strongly sheared samples.