Superposed deformation and its implication to the geologic history of the Ellsworth Mountains, West Antarctica

• Main Author: Yoshida, Masaru
• Language: English
• Published: 1982
• Subjects: Borchgrevink; Ellsworth Mountains; Heritage Range; West Antarctica; Antarc*; Antarctica; Memoirs of National Institute of Polar Research; Polar Research
• Online Access: https://nipr.repo.nii.ac.jp/record/1247/files/KJ00000011773.pdf

P(論文) Based on the 1979-1980 field survey, preliminary results of stratigraphic, tectonic, metamorphic, and whole rock K-Ar dating studies of the southern part of the Heritage Range are given. Assembling all the results, the following scheme of a polyorogenic sequence is represented as a first approximation, along with possibilities of some other interpretations. i) The Precambrian events exemplified only by the K-Ar age of 935Ma are problematically taken for as indicating a fragment of the Precambrian basement. ii) Metamorphic recrystallization under the low grade conditions of WINKLER (Petrogenesis of Metamorphic Rocks, N.Y., Springer, 1974), formation of main cleavages and longitudinal reclined and inclined isoclinal and longitudinal nearly horizontal close folds occurred after the Heritage Group (Middle to Upper Cambrian) and before the intrusion of altered dolerite dikes with minimum ages of ca. 400Ma. These events are referred to either possibly the early Borchgrevink Orogeny, or more probably, the Ross Orogeny. iii) Low grade metamorphic recrystallization, and formation of part of the closely spaced cleavages and longitudinal kink folds occurred after the Crashsite Quartzite (?pre-Devonian to Devonian) and before or during the Whiteout Conglomerate (?Permo-Carboniferous), at around the age of 300Ma. These events are referred to the late phase of the Borchgrevink Orogeny. iv) Very low grade metamorphic recrystallization, formation of roughly spaced cleavages, longitudinal open folds and transverse gentle folds occurred after the Polarstar Formation (Permian). Maximum K-Ar age of 235 Ma is considered to reflect these events which are referred to the early Mesozoic Ellsworth Orogeny. departmental bulletin paper