長野県鹿教湯(かげゆ)温泉周辺の新第三系と変質作用

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The stratigraphy of the Neogene System and its rock alteration in the area of Kageyu spa, north central Nagano Prefecture, are studied from the viewpoint of volcano-stratigraphy. The abundant volcanic rocks together with pyroclastic fall deposits, accumulated in the age from early to late Miocene, are widespread in this area. The volcanco-stratigraphical sequence is shown in the following table. The table clearly shows that the igneous activity consists of three cycles, each of which regularly begins in basic volcanism and ends in acidic one. The rock alteration is classified into the following two types. 1) Alteration through diagenetic process 2) Alteration through syngenetic process which is accompanied with the volcanism of the first type alteration, the "albite-chlorite zone" is recognized in the Uchimura formation, and is well distinguished from the zeolite facies recognized in the upper beds. As to the zeolite facies, the Hosoonotaki andesite [Table] member corresponds roughly to the "mordenite zone" and the Ichitoge plagio-liparite member to the "clinoptilolite zone" respectively. Though laumontite and analcite are found in basic rocks the "laumontite zone" of COOMBS et al. (1960) is not recognized in this district. Because they occur only as amygdaloidal minerals and are undoubtedly the products of the second type alteration. Except these two zeolite minerals, characteristic minerals of the second type alteration are thomsonite, natrolite, actinolite, epidote, dolomite and calcite. There is something common between the two types of alteration, because chemical composition of original rocks have significant influence upon the mineral assemblage of the alteration products.
日本地質学会の論文
1973-07-01

長野県鹿教湯(かげゆ)温泉周辺の新第三系と変質作用

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