Chemical Characteristics of Biotites and Hornblendes from Metamorphic Rocks around Lutzow-Holmbukta, East Antarctica

概要

論文の詳細を見る
Chemical compositions of biotites and hornblendes in metamorphic rocks around Lutzow-Holmbukta show that these minerals have the characteristics of granulite facies ones. Some low-Ti biotites and hornblendes may be due to low TiO_2 content of host rocks. Chemical natures of biotites and hornblendes reflect those of their host rocks, that is, biotites from metabasites are phlogopite and Na_2O-rich ones, while those from paragneisses are Fe-rich and Na_2O-poor ones. The replacement of R^<2+> by R^<3+> ions in octahedral sites in biotites increases from metabasites through charnockites to paragneisses. Hornblendes from metabasites are richer in Na_2O than K_2O, but the proportion is reversed in hornblendes from charnockites and hornblende gneisses. The values of log (ƒ_<H_2O>/ƒ_<HF>) of fluid phase coexisting with biotites during crystallization are 4.3 in metabasites and 3.8 in paragneisses, respectively. From the available data of the F content of hydrous minerals in various metamorphic terrains, it can be presumed that the ratio of ƒ_<H_2O>/ƒ_<HF> decreases during progressive metamorphism.
国立極地研究所の論文