| 概要 |
The Chikugo metamorphic rocks are mainly composed of black schists, sandstone schists, green schists, small amounts of quartz schists and metamorphosed gabbroic intrusive rocks. No conglomerate and ca...lcareous schists are found. The metamorphic rocks are gently folded and have two pairs of anticlinal and synclinal axis plunging from 5 to 7 degrees to the east. The Chikugo metamorphic rocks are intruded by granitic rocks of the Cretaceous age into their anticlinal parts and affected by the contact metamorphism. Four zones of metamorphism, A_1, A_2, B_1, B_2, are distinguished in the metamorphic area. Some ambiguitities, however, are present in defining the zone B2, because the rock of this zone may be affected by the granitic intrusions. There is no critical fact to distinguish them from the regional metamorphism. The zone A1 is confined to the gabbroic intrusions, characterrized by the presence of clinopyroxene, brown hornblende, pumpellyite and alkali amphibole. Mineral assembrages, epidote-pumpellyite-actinolite-diopside and chlorite-actinolite-epidote-brown hornblende, and a limited occurrence of alkali amphiboles to the central part of the northern half of the gabbroic intrusions, indicate water deficient conditions of this zone comparing to its neibouring schistose area. The zone A_2 is distinguished from the zone A_1 by the absence of clinopyroxene and brown hornblende, and from the zone B_2 by the presence of pumpellyite. The zone B_2 is characterized by the relatively wide occurrence of biotite in pelitic and samitic schists. The distribution of the metamorphic zones indicates that the metamorphic grade increases to the north. The occurrences of alkali amphiboles and the sporadical distribution of biotites in the whole metamorphic area indicate a water deficient condition. The zonal structure of alkali amphiboles with actinolite, that is, in the zone A_1 alkali amphibole occurs at the periphery and in the zone B_1 at the core, seems to indicate that the water pressure increases towards the north. Pressure-temperature conditions of the metamorphic rocks are limited by the stable occurrence of albite and also may be indicated by the widespread occurrence of biaxial calcite.続きを見る
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Mendeley出力
