Comparative study on the major element chemical compositions of Antarctic chondrites to those of non-Antarctic falls with reference to terrestrial weathering

• Main Authors: Tetsuya Nobuyoshi, Hiroshi Haramura, Yukio Ikeda, Makoto Kimura, Hideyasu Kojima, Naoya Imae, Min Sung Lee
• Format: Report
• Language: English
• Published: Department of Earth Sciences, Ibaraki University/Department of Meteorites, National Institute of Polar Research/Department of Earth Sciences, Ibaraki University/Department of Earth Sciences, Ibaraki University/Department of Meteorites, National Institute of Polar Research/Department of Meteorites, National Institute of Polar Research/Department of Earth Sciences, Seoul University 1997
• Subjects: Antarctic; The Antarctic; Antarc*
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=5896; http://id.nii.ac.jp/1291/00005896/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=5896&item_no=1&attribute_id=18&file_no=1

Antarctic ordinary chondrites contain variable amounts of Fe_2O_3 and water as terrestrial weathering products. The Fe_2O_3 contents have a positive correlation with water contents, and a negative correlation with metallic Fe. Therefore, oxygen and water were added to Antarctic chondrites during weathering to form limonitic alteration from metallic iron. Other major elements and total Fe slightly decrease with increasing Fe_2O_3. This decrease is caused by the "dilution" effect due to additional water and oxygen, suggesting that most of the Antarctic chondrites seem to have undergone terrestrial weathering in a quasi-closed system insofar as major elements are concerned. Weathering index has minimal or no relation with the Fe_2O_3 contents of chondrites. Extensive weathering obscures petrographic features of some chondrites, leading to the misclassification, and they are revised on the basis of UC diagram. The major element compositions of Antarctic ordinary chondrites are the same as those of non-Antarctic falls, and they show slight difference in Mg and Na contents among H, L, and LL chondrites; H chondrites have the highest Mg/Si ratio and the lowest Na/Si ratio on average. Some LL chondrite breccias have higher K contents than non-brecciated LL chondrites.