丹澤山地箒澤附近の石英閃綠岩類貫入にともなった混成現象について

On the Hybridism Related to the Intrusion of Quartz-Dioritic Complex in the Vicinity of Hôkizawa, Tanzawa Mountainland, Kanagawa Prefecture, Japan.

Kojima George

廣島大學地學研究報告

Geological report of the Hiroshima University

Three types of metamorphism are distinguished from each other in relation to the intrusion of quartz-dioritic complex. In the vicinity of Hôkizawa, the igneous complex is mainly composed of hornblende-quartz-diorite (P1. I, fig. 1) and hornblende-biotite-granodiorite (P1. I, fig. 2). The related minor rock masses, such as pegmatites and aplites, are also found in and near the major complex. To the south of the boundary of igneous complex, there develop metamorphic rocks derived from Misaka Series, which are believed to be Lower Miocene in age. The metamorphic facies of Misaka Series was studied by K. Sugi 1) in detail. Near Hôkizawa, the igneous complex comes in contact with plagioclase-hornblende-schists (Pl. I, fig. 3) of amphibolite-facies.
The metamorphism related to the formation of plagioclase-horndlende-schists was carried out under the condition of componental differential movement and the introduction of heat and materials ("emanations"), which are to be considered as a fore-runner of the intruding quartz-dioritic magma.
The second phase of metamorphism is the direct thermal and material effect of the intruded quartz-dioritic magma to plagioclase-amphibolites and bytownite-hornblende-gabbroic rock (Pl. Ⅱ, fig. 3), occurring as wall rocks and xenoliths. Plagioclase-hornblende-schists lose the schistosity, and are changed to granoblastic aggregates of plagioclase and hornblende (Pl. Ⅱ, fig. 1). Near the very junction, the assimilation of plagioclase-amphi-bolites (Pl. Ⅱ, fig. 2)and bytownite-hornblende-gabbroic rock (Pl. Ⅲ, fig. 1) is also observed.
The third phase of metamorphism is represented by the metasomatic change of common green hornblende to cummingtonite and the sodification of plagioclase feldspars. At the later stage of solidification of quartz-diori-tic magma, as a result of excessive separation of hornblende and lime-rich feldspars, the residual solution was enriched stoichiometrically of alumina, magnesia, iron, soda, and silica, compared with lime. At this stage, the residual solution reacted on the already crystallized hornblende and plagio-clase feldspars, resulting in the formation of cummingtonite (Pl. Ⅲ, fig. 2&3) and sodic feldspars.
1)K. Sugi, Jap. Journ. Geol. Geogr, 9 (1931), P. 87.

jpn

廣島大學理學部地學教室

[ISSN] 0073-2303

[NCID] AN00213676