Petrological study of the Tabashine adamellite mass

Abstract

The Tabashine adamellite mass intruded into the black slates, conglomerates of the Toyoma series and basic volcanics probably of Cretaceous. As the results the country rocks have been metamorphosed into various kinds of hornfels. From the mode of occurrence and petrographical feature, this mass can be divided to the following four rock types; Tabashine, Aikawa, Togaku and Kuromori types.
Tabashine type is chiefly adamellite. Aikawa and Togaku types are granodiorite. Kuromori is quartz diorite.
All but Kuromori type have dark inclusions, which are similar to the Kuromori type in petrographical properties. All rock types have nearly same essential constitutent minerlas, i. e., plagioclase, orthoclase, quartz, biotite, hornblende, and augite and/or hypersthene.
Most of plagioclases are oligoclase, and orthoclases are perthitic. γ of biotite vary from 1.645 to 1.660.
Some consideration on the petrogenesis is given. The hybrid phenomer a between the granitic magma and the diabasic rock of this area have been studied by Yamada (1939). Contrary to his argument, it is to be noted that the effect of such hybridization on the basification of granitic rock is less significant than that between granitic magma and basic rock (probably two pyroxene gabbroic rock) at a deeper zone of the crust.
This original granitic magma may be adamellitic in composition. Kvrcmori type and dark inclusion may be the products of such phenomenon, and granodiorites as Aikawa and Togaku type may have been resulted when hybridization proceeded further. When compared with the Orikabe and Hirota masses to the east, they have closely similar geological situation and petrographical properties to the Tabashine mass.