Petrography and geothermometry-geobarometry of Botnnuten, East Antarctica

• Main Authors: Yoichi Motoyoshi, Kazuyuki Shiraishi
• Format: Report
• Language: English
• Published: Department of Geology and Mineralogy, Faculty of Science, HokkaidoUniversity/National Institute of Polar Research 1985
• Subjects: Botnnuten; East Antarctica; Yamato; Antarc*; Antarctica; Memoirs of National Institute of Polar Research; Polar Research
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=1789; http://id.nii.ac.jp/1291/00001789/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=1789&item_no=1&attribute_id=18&file_no=1

Botnnuten is an isolated nunatak situated between Lutzow-Holm Bay and the Yamato Mountains, East Antarctica. It is composed of well-layered pelitic and basic gneisses with subordinate amounts of calc-silicate rock. The petrographical examinations revealed that the assemblages of sillimanite+Kfeldspar+biotite in the pelitic gneiss, and garnet+clinopyroxene+orthopyroxene+plagioclase+quartz in the basic gneiss are observed to have coexisted stably. Sillimanite+spinel assemblage included in porphyroblastic garnet is totally interpreted to be a breakdown product after staurolite during the prograde recrystallization. The present phase relations and geothermo-barometries yielded the metamorphic conditions of Botnnuten rocks to be 750-800℃ at 5-6 kbars. On the basis of the petrographical features with respect to the occurrence of aluminous silicate minerals and the recrystallization history inferred from the textural relationships, and the P-T conditions mentioned above, it is concluded that Botnnuten is a low-pressure portion of the Lutzow-Holm Complex.