STRUCTURAL EVOLUTION OF RUNDVAGSHETTA REGION, LUTZOW-HOLM BAY, EAST ANTARCTICA

• Main Authors: イシカワ マサヒロ, モトヨシ ヨウイチ, / カワサキ トシスケ, Masahiro ISHIKAWA, Yoichi MOTOYOSHI, Geoffrey L. FRASER, Toshisuke KAWASAKI
• Format: Report
• Language: English
• Published: Institute of Geology and Paleontology, Faculty of Science, Tohoku University 1994
• Subjects: East Antarctica; Rundvagshetta; Antarc*; Antarctica
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=2753; http://id.nii.ac.jp/1291/00002753/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=2753&item_no=1&attribute_id=18&file_no=1

The highest grade part of the Lutzow-Holm Complex crops out on the southern coastline of Lutzow-Holm Bay in East Antarctica. Orthopyroxene+sillimanite±quartz assemblages reveal high-T, high-P conditions for peak metamorphism of granulites of Rundvagshetta. Moreover, their fabrics imply regional ductile deformation during peak metamorphism, which was characterized by the formation of a WNW-ESE subhorizontal mineral lineation and the development of high-strain structures such as isoclinal buckling folds (F_n) and boudinage (B_n and B_m). The high-strain deformation was followed by the development of symplectic intergrowths of cordierite±sapphirine±spinel around sillimanite and orthopyroxene, and symplectic intergrowths of orthopyroxene+cordierite±sapphirine around garnets in response to decompression. There is little symplectic intergrowth strained intensely, whereas strained cordierite is locally observed. It implies that the regional high-strain deformation had ceased before the time of the reactions orthopyroxene+sillimanite+quartz=cordierite, orthopyroxene+sillimanite=cordierite+sapphirine±spinel, garnet=orthopyroxene+cordierite+sapphirine and garnet+quartz=orthopyroxene+cordierite. In contrast to the peak metamorphic high-strain deformation, the post-peak metamorphic structural evolution was characterized by low-strain and localized deformations such as F_<n+1> gentle folding, emplacement of clinopyroxene pegmatites and basic dykes, and local shearing in the N-S compressional and E-W extensional field. In response to subsequent N-S compression, ductile thrusting had taken place. The last structural event at Rundvagshetta was represented by the emplacement of felsic pegmatites.