Nd AND Sr ISOTOPE CHARACTERISTICS OF THE PLUTONIC ROCKS IN THE SØR RONDANE MOUNTAINS, EAST ANTARCTICA

• Main Authors: アラカワ, ヨウジ, タカハシ, ユウヘイ, タイノショウ, ヨシアキ, ARAKAWA, Yoji, TAKAHASHI, Yuhei, TAINOSHO, Yoshiaki
• Language: English
• Published: National Institute of Polar Research 1994
• Subjects: East Antarctica; Nils; Sør-Rondane; Sør Rondane Mountains; Vikinghøgda; Lunckeryggen; Pingvinane; Mefjell; Nils Larsen; Rogerstoppane; Antarc*; Antarctica
• Online Access: https://nipr.repo.nii.ac.jp/record/2751/files/KJ00002368381.pdf; https://doi.org/10.15094/00002751; https://nipr.repo.nii.ac.jp/records/2751

P(論文) Plutonic rocks in the Sør Rondane Mountains, East Antarctica comprise early Paleozoic granitic rocks and late Proterozoic tonalite. The former is further classified into two types (volcanic arc type and within plate type). The initial εNd values for the analyzed granitic rocks (six samples from volcanic arc type and one from within plate type) fall in a limited range (-1.48 to +0.62) and Nd model ages (T_<DM>) for the granitic rocks were estimated to be 900-1000 Ma which agree well with the ages of basement rocks. Taking Sr isotope data and element compositions into account, volcanic arc type granites (Dufek, Lunckeryggen and Mefjell) are explained by a fractional crystallization from an isotopically homogeneous magma which was generated from late Proterozoic lower (to middle) crustal rocks, whereas the within plate type granites (Vikinghøgda, Rogerstoppane and Pingvinane) are assumed to have been formed mainly by mixing between crustal rocks with high Sr isotope ratios and mafic (to intermediate) parental magma originated in the upper mantle or lower crustal source. The presence of extremely high Sr isotope ratios for the within plate type granites suggests the involvement of more older crustal rocks (early to middle Proterozoic) beneath the Sør Rondane Mountains. Changes of magma sources and a dominant process of magma formation from within plate type granites (early) to volcanic arc type granites (late) reflect the change of tectonic situation in this region during the early Paleozoic. The late Proterozoic Nils Larsen tonalite was generated in a depleted mantle and evolved without large crustal contributions. departmental bulletin paper