東赤石山橄欖岩體(超鹽基性岩にともなわれる尖晶石の研究 その2)

抄録

Higashi Akaishi-yama, which is composed of dunite, is situated in the Sambagawa metamorphic zone in the northern part of Shikoku., Structurally, the dunito mass can be divided into eastern and western parts, and the constituent rocks of each part are different., The eastern mass is composed of spinel bearing dunite, pyroxene peridotite, eclogite and chromite ore with a well defined banded texture., Spinel crystals, as an accessory component of the dunite facies in the eastern mass always contain much chromite, usually about 40% Cr₂O₃ by weight., The western mass is composed of spinel bearing dunite and pyroxene peridotite, but neither eclogites nor banded chromite ore have been found in it., The spinel crystals in the western mass contain very little Cr₂O₃, at the most about 16% by weight., Comparison of the chemical composition of the chromite crystals in 'the banded ore with the chromite crystals in the country rock show, the weight percent of the Cr₂O₃ in the ore to be 50% more or less, and that of the country rocks is usually 40% or less., It is believed that the accumulation of the chromite crystals has had influence on their own chemical composition.,