EXPERIMENTAL STUDIES ON SYENITIC ROCKS IN THE YAMATO MOUNTAINS, EAST ANTARCTICA

• Main Authors: オオバ タカノブ, シライシ カズユキ, Takanobu OBA, Kazuyuki SHIRAISHI
• Format: Report
• Language: English
• Published: Department of Geoscience, Joetsu University of Education 1993
• Subjects: East Antarctica; Yamato; Antarc*; Antarctica
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=2720; http://id.nii.ac.jp/1291/00002720/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=2720&item_no=1&attribute_id=18&file_no=1

The stability of amphibole was studied in the presence of syenite composition liquid. The melting relationships of three hornblende clinopyroxene quartz syenites and a hornblende two-pyroxene syenite from the Yamato Mountains were determined in the temperature range of 650-900℃, under a water pressure of 0.05-0.3GPa and oxygen fugacities of the FMQ buffer. Experimental results of hornblende clinopyroxene quartz syenites (Y406 and Y904) and one hornblende two-pyroxene syenite (Y557) at 0.1 GPa show that melting begins between 720℃ and 770℃, and amphiboles disappear between 810℃ and 895℃. With the increasing temperature at 0.1GPa, quartz disappears first, then plagioclase and amphibole in that order. The water saturated solidus temperature of a normative quartz-free hornblende clinopyroxene mela-syenite (Y405) is about 780℃ at 0.1GPa. K-feldspar in this sample disappears at lower temperature than amphibole. In two syenites (Y557 and Y904), solidus and the stability limit line of amphibole intersect at a lower pressure than 0.3GPa. Moreover, all rocks investigated are at least 40% melted at temperatures ∿50℃ above the solidus. The present results suggest that amphibole in these syenites could crystallize at pressures lower than 0.3GPa (∿10km in depth), indicating their emplacements at a relatively shallow crustal level.