セイシェル諸島の花崗岩中の角閃石(<特集II.>角閃石研究の現状と課題-地団研第37回総会造岩鉱物シンポジウム-)

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Late Precambrian granitic rocks found from Mahe Islands in the Seychelles Archipelago comprise three types of rock-series: (1) gneissose granodiorite-gneissose tonalite and amphibolite-leucogranite series, (2) grey granite-gneissose grey granite series, and (3) pink granite-porphyritic granite series. (1) Gneissose granodiorite contains magnesio-hornblende which is poor in alkalis and is weakly pleochroic. (2) The rocks of the grey granite-gneissose grey granite series belong to the alkali granite and contain characteristically mesoperthite, ferro-barroisite, riebeckite, ferro-actinolite, ferro-richterite and fluorite. Ferro-barroisite in the grey granite is strongly pleochroic and is of small negative optical angle. Ferro-barroisite is commonly rimmed with riebeckite. Ferro-actinolite with smaller negative optical angle is sometimes found in the core part of the ferro-barroisite. Ferro-richterite in the gneissose grey granite is strongly pleochroic and is of small negative optical angle. Riebeckite occurs as a shell of the ferro-richterite and it also occurs as a radial aggregate along the grain boundaries between mesoperthite and quartz grains. Fe^<2+>/(Fe^<2+>+Mg) atomic ratios in the amphiboles of the second series granite are remarkably high. (3) Pink granite contains Mn-rich ferro-edenite which is moderately pleochroic and is of small negative optical angle. Porphyritic granite contains ferro-hornblende which is moderately pleochroic. It is found that the Seychelles amphiboles are formed sensitively depending on the bulk chemical composition of their host rocks. The occurrence of the ferro-barroisite and ferro-richterite rimmed with riebeckite, as found in the Seychelles alkali granites, is extraordinally rare.
地学団体研究会の論文
1984-09-25

セイシェル諸島の花崗岩中の角閃石(<特集II.>角閃石研究の現状と課題-地団研第37回総会造岩鉱物シンポジウム-)

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