岡山県中・南部の花崗岩類

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Granitic rocks in central to southern part of Okayama Prefecture are believed, with some chronological data, to be products of Late Mesozoic. The writers grouped them into 5 rock-types which are called type I, type II, type III, type IV and fine-grained type respectively. The type I is called biotite granite and shows equigranular texture. The other types are called hornblende-biotite adamellite which commonly shows porphyritic or glomeroporphyritic texture characterized by any of felsic minerals: i.e., K-feldspar characterizes the type II, quartz characterizes the type III and plagioclase characterizes the type ？. The geological relations between the different types of granite have not always been clarified. All types of granite are probably transitional to each other, though on the geological map they are bounded by faults and/or roof-pendants. The perthitic structure is very common in K-feldspars in all granite types. K-feldspars in the type I are often triclinic in crystal system but those in the other types are always monoclinic. K-feldspars in the type III seem to be highly disordered in structural state as compared with the others. The writers inferred from X-ray study of K-feldspars that perthites in the type I would be often fully exsolved but those in the other types would be often incompletely exsolved. These evidences may suggest that granite of type I is solidified more slowly than the other types of granite. The granite of type III may be a subvolcanic granite.
日本地質学会の論文
1979-09-20

岡山県中・南部の花崗岩類

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