わづかに熱変成した火山岩中の斜長石双晶の特長,及びその岩石学えの応用について

概要

論文の詳細を見る
In his recent study the writer discovered a differences between the plagioclase twinning of the igneous rocks and that of the metamorphic rocks, and proposed a new method (plagioclase twin method) for the study of "granite problem". In the present paper are described the features of plagioclase twinning in some slightly contact-metamorphosed basic effusives (meta-basalts and meta-andesites). The groundmass plagioclases of these meta-volcanics are richer in untwinned plagioclases and poorer in A-twins comparing with those of non-metamorphosed basic effusives, the amounts of C-twins being not so different. As to the phenocrysts, however, there are no such differences in the mode of twinning between these two types of effusive rocks (Fig. 1). The explanation seems to be sought in the disappearance of twinning (albite law) in some A-twins of groundmass plagioclases due to thermal metamorphism. Thus the features of plagioclase twinning may be used as a clue to determine the thermal effect operated upon slightly contact-metamorphosed effusives rocks. On that basis the so-called basic (or dark) inclusions in some granodiorites of southern Abukuma Plateau are explained as xenoliths derived from some diabases or allied basic igneous rocks (Fig. 6).
横浜国立大学の論文
1952-03-25