海洋地域の岩石 : I.高アルミナ玄武岩

概要

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This paper is written to critisize the concept of high-alumina basalt recently proposed by H. KUNO (1960; 1965). He has considered that the highaim ina basalt is of intermediate character between the tholeiitic and alkali basalts. Many tholeiitic basalts have been hitherto dredged from such oceanic ridges as East Pacific Rise, Mid-Atlantic Ridge and Mid-Indian Ridge, as shown in Table 1. Detailed examination on the chemistry of these tholeiitic basalts led the present writters to the following conclusions: 1. The tholeiitic basalts dredged from the oceanic ridges differ from those of the oceanic islands. The former has much higher alumina and lower titania than the latter. This relation is clearly shown in Fig. 1. 2. The high-alumina basalts are not of intermediate character between the tholeiitic and alkali basalts, but are rather of tholeiitic affinity as evident from Figs. 4, 5, and 6. The writer thinks that KUNO made a mistake by his erroneous generalization of the results in the Izu-Hakone province in central Japan to the other provinces. 3. Regardless of KUNO'S concept on the high-alumina basalt, the existence of high-alumina basalts is evident in oceanic and other regions. The researches on the physico-chemical conditions under which the high-alumina basalts are built must explain the predominance of these basalts on the oceanic ridges.
地学団体研究会の論文
1968-01-25