TILTING MOVEMENT OF SØR RONDANE MOUNTAINS AND POSSIBLE APPARENT POLAR-WANDER PATH FOR PRECAMBRIAN TO CAMBRO-ORDOVICIAN FROM NILS LARSENFJELLET

• Main Authors: トキエダ カツヤス, フナキ ミノル, Katsuyasu TOKIEDA, Minoru FUNAKI
• Format: Report
• Language: English
• Published: Department of Physics, Faculty of Sciences, Shimane University 1991
• Subjects: East Antarctica; Tilting; Nils; Sør-Rondane; Sør Rondane Mountains; Brattnipene; Lunckeryggen; Pingvinane; Nils Larsenfjellet; Antarc*; Antarctica; Geomagnetic Pole
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=2688; http://id.nii.ac.jp/1291/00002688/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=2688&item_no=1&attribute_id=18&file_no=1

Alternating field demagnetizations were performed for 479 hand samples (32 sites) collected from the Sør Rondane Mountains, East Antarctica. Clear convergence of natural remanent magnetization (NRM) was observed for only 82 samples (17%) from 8 sites. They were dolerites, tonalites, syenites and hornblendites, all having NRM strength more than 10^<-6>Am^2/kg. Samples less than 10^<-7>Am^2/kg, including granites, granitic rocks and granitic dike or vein, yielded no paleomagnetically significant results. The virtual geomagnetic pole positions (VGP) from 1550 nunatak dolerite, Brattnipene dolerite and Lunckeryggen syenite fall on a fairly small area, well matching with reported ones from Pingvinane granite and some rocks in the Sør Rondane Mountains. Their radiometric ages are confined to early Ordovician. On the other hand, the Ordovician VGPs from elsewhere in East Antarctica are significantly deviated from those from the Sør Rondane Mountains These facts lead us to a conclusion that the mass of the Sør Rondane Mountains was undeformed locally, but tilted as a whole relatively to the rest mass in East Antarctica. A Precambrian VGP, 60.4°S, 21.5°W in 662±23 Ma, was estimated from magnetically cleaned remanences and a newly determined ^<40>Ar-^<39>Ar age of Nils Larsenfjellet tonalites, with further proposing of an apparent polar-wander path (APWP) for Precambrian to Cambro-Ordovician from Nils Larsenfjellet. No attempt of thermal demagnetizations and other methods of the rockmagnetism have been done to verify the quality of the magnetically cleaned remanence. A serious paleomagnetic significance is provided, however, with the fact that the analogous VGPs were obtained from a variety of rocks of similar ages.