| 概要 |
The order of crystallization of minerals in the melts of the Matsuura basalts was investigated under well controlled conditions of temperature and oxygen partial pressure ranging from 1100° to 1350°C ...and from 10^-0.7 to 10^-9.0 atm, respectively. The primary phases are iron oxides at the oxygen partial pressures of 10^-0.7 to ^10-7.0 atm, while they are olivine and clinopyroxene at the pressures of 10^-7.0 to l0^-9.0 atm for the tholeiitic starting materials (Sp. 2, Sp. 21). On the other hand, for the alkali basaltic starting material (Sp. 138) iron oxides appear first at the pressures of 10^-0.7 to 10^-7.0 atm, while plagioclase crystals appear first below 10ー7.oatm oxygen partial pressure. The change from olivine+ clinopyroxene to plagioclase of the primary phase assemblage below 10^-7.0 atm occurs when chemical composition comes to that of one of the alkali basalts (Sp. 47), as the chemical composition changes from tholeiitic to alkalic. These results are well in accord with the features of the natural bas~lts observed under the microscope. It is interesting that the order of crystallization of plagioclase followed by olivine +clinopyroxene reverses with decreasing oxygen partial pressure. This phenomenon is also accompanied with change of chemical composition of the glass, caused by the crystallization of iron oxides, which is affected by oxygen partial pressure.続きを見る
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Mendeley出力
