尖閣列島黄尾礁の火山岩

概要

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The results of the geological and petrological study of the basaltic rocks from Kobi-sho in the senkaku-retto, are summarized as follows. 1. The Kobi-sho volcano is an insular volcano with a few of perfect craters consisting of stratovolcano. The activities of this volcano may be in Pleistocene time. 2. Essential constituent minerals are olivine, augite and plagioclase phenocrysts or microphenocrysts and in addition to these minerals, the groundmass anorthoclase and magnetite and glass. They are augite olivine basalt, and mafic mineral assemblages of these basaltic rocks belong to IVb or IVb→c type. 3. Their chemieal and normative mineral compositions are shown in Table 1. Generally, they are rich in CaO, while poor in Al2O3 and TiO2 (Fig. 3). These basalts contain 0.84～ -0.24% of normative quartz. In the alumina-total alkalies-silica relation diagram, they are plotted in the area of alkali basalt area. Alkali content of these basalts are intermediate between KUNO's high-alkali tholeiite and alkali rock in the total alkaies and silica diagram (Fig. 4). Other petrochemical characters of these basalts are shown in the normative or-ab-an, wo-en-fs, wo-fo-Q, Q-fo-fa and MgO-(FeO+Fe2O3)-(Na2O+K2O) diagrams.
〔長崎大学教養部〕の論文