Petrographic Studies of Potash Feldspar from the Yamato Sanmyaku, East Antarctica

• Main Authors: オオタ ヨシヒデ, キザキ コウシロウ, Yoshihide OHTA, Koshiro KIZAKI
• Format: Report
• Language: English
• Published: Mineralogisk Geologisk Museum 1966
• Subjects: East Antarctica; Yamato; Kizaki; Prins Harald Kyst; Yamato Sanmyaku; Antarc*; Antarctica
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=65; http://id.nii.ac.jp/1291/00000065/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=65&item_no=1&attribute_id=18&file_no=1

The Yamato Sanmyaku is a mountain range located about 200km south of Prins Harald Kyst, East Antarctica. The mountains are composed of charnockitic group and granitic group rocks which were described geologically and petrographically by K. KIZAKI (1965). The present paper deals with the potash feldspars from the charnockitic group and pegmatites. The occurrence of the potash feldspars and their optical characteristics are described first, revealing the mechanism of albitization of potash feldspars which have a wide range in the optical axial angle. Next, the two-feldspar geothermometry method is applied to the potash feldspars from the Yamato Sanmyaku and the results are compared with that of the Norwegian potash feldspars and also with the data of Japanese plutonic rocks. The formation temperatures estimated from the distribution coefficient k, triclinicity and 2Vx value are discussed on the basis of the subsolidus phase relation, the relation between the formation temperature and crystal symmetry, and the relation between the optical axial angle and triclinicity. These relations well support the conclusion held from the geological and petrographical points of view that the charnockitic rocks were originally formed under a granulite facies condition, but their characters were influenced more or less by the subsequent granitization under an amphibolite facies condition.