静岡県高草山地域のアルカリ岩類
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概要
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The Takakusayama formation consists mainly of rocks of alkali rock series, that are intruded into the Setogawa group. Most of these rocks, however, are now in contact with the latter with steep faults. Its igneous activities are divided, in ascending order, into quartz syenite rocks, Takakusayama alkali rocks I, Takakusayama alkali rocks II and Miwa clastic rocks. The Takakusayama alkali rocks I is constituted by alkali basalt lava flow including pyroclastic rocks and mudstone, and trachytic andesite as a final product of differentiation. The sequence of intrusion of Takakusayama alkali rocks II seems to be the alkali basalt, trachytic basalt, trachytic andesite and trachyte with continuous change of chemical composition. The volcanic centers of Takakusayama formation migrated gradually toward the south-southwest side. In Osaka district the Takakusayama alkali rocks II is intruded by some dikes of two-pyroxene andesite, the age of which corresponds with or is after that of sedimentaion of the Miwa clastic rocks. The olivine gabbro, trending from SSW to NNE, cuts the Setogawa group and the Takakusayama alkali rocks I at northern Simonoya. Also several types of dikes such as teschenite, titanaugite-aegirine-augite gabbro, quartz-bearing dolerite are related with the igneous activity. Fifteen samples of these alkali rocks were analysed. The contents of SiO_2 show approximately 45-65%. The chemical compositions of rocks are characterized by higher Na_20, Fe_2O_3 and lower K_20, Ti0_2, P_2O_5, FeO, Fe0+Fe_2O_3 contents, as compared with the Circum Japan Sea Alkali Rock Series. However, the Takakusayama alkali rocks I shows lower K_O and higher MgO contents than the Takakusayama alkali rocks II. It is suggested that these rocks originated from one parent magma with alkali basalt character.
- 日本地質学会の論文
- 1976-12-30
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