Staurolite and kyanite in the Takanuki pelitic gneisses of the Abukuma metamorphic terrane northeast Japan
Staurolite and kyanite in the Takanuki pelitic gneisses of the Abukuma metamorphic terrane northeast Japan
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日本东北部阿武隈变质地体 Takanuki 泥质片麻岩中的十字石和蓝晶石
DOI：
10.2465/ganko.84.141
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发表时间：
1989
期刊：
影响因子：
--
通讯作者：
S. Kishi
中科院分区：
文献类型：
--
作者：
Y. Hiroi;S. Kishi
在Takanuki附近三个地点的硅线石+钾长石带富石英泥质片麻岩中，新发现了残留的十字石和含或不含富锌尖晶石的亚稳蓝晶石。它呈无面体颗粒，直径可达0.2毫米，完全包含在斜长石单晶中，比附近硅质不饱和变质岩中的刚玉石富锌，氧化锌含量高达2wt%。泥质片麻岩中残留的刚玉不表现出石榴石+硅线石+尖晶石组合的破裂结构，这在变质岩中是明显的。这可能主要是由于泥质片麻岩中斜长石单晶中残留的硬沸石周围局部存在较高的H2O分压，这是由于微量的硬沸石脱水所致。另一方面，与富锌尖晶石伴生的蓝晶石可能是在斜长石晶体晶界上的十字石之后形成的，因为十字石释放出的H2O可以沿着晶界逃逸。这反过来又表明，一些蓝晶石是在没有石英的情况下，由十字石破裂而形成的。
Relict staurolite was newly found, together with metastable kyanite with or without Zn-rich spinel, in the sillimanite+K-feldspar zone grade quartz-rich Takanuki pelitic gneisses at three localities near Takanuki. It occurs as anhedral grains, up to 0.2mm in diameter, completely included in plagioclase single crystals, and is much Zn-richer, containing up to 2 wt. % ZnO, than staurolites in the nearby silica-undersaturated metalateritic rocks. The relict staurolites in the pelitic gneisses do not show any breakdown texture to the garnet+sillimanite+spinel assemblage, which is conspicuous in the metalateritic rocks. This may be due mainly to the high partial pressure of H2O locally prevailed around relict staurolites within plagioclase single crystals in pelitic gneisses, that resulted from dehydration of a trace amount of staurolite. On the other hand, kyanite associated with Zn-rich spinel may have been formed after staurolite which was located at the grain boundary of host plagioclase crystals, because H2O released from staurolite could escape along the grain boundary. This, in turn, suggests that some kyanite was formed as a product of staurolite breakdown in the absence of quartz.