Shape of Fe-Ni grains and magnetic susceptibility anisotropy in Antarctic chondrites

• Main Authors: Naoyuki Fujii, Keisuke Ito, Masamichi Miyamoto, Yozo Hamano
• Format: Report
• Language: English
• Published: Department of Earth Sciences, Faculty of Science, Kobe University 1983
• Subjects: Antarctic; Antarc*; Antarctica; Memoirs of National Institute of Polar Research; Polar Research
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=1577; http://id.nii.ac.jp/1291/00001577/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=1577&item_no=1&attribute_id=18&file_no=1

Magnetic susceptibility anisotropy is measured for various petrologic types of ordinary chondrites from Antarctica, which are three H types : ALH-77233 (H4), ALH-77182 (H5) and ALH-77115 (H6); four L types : Y-74191 (L3), ALH-77230 (L4), ALH-77254 (L5) and ALH-77231 (L6); and four LL types : Y-75258 (LL6), Y-790519 (LL), Y-790723 (LL) and Y-790964 (LL). The last three are shock-melted chondrites and have high strengths, whereas Y-75258 has a very low strength. Magnetic susceptibility anisotropy appears to be low for LL chondrites and seems to bear no correlation with porosity and petrologic types among H and L chondrites. Both prolate and oblate susceptibility ellipsoids are obtained. To characterize the shape irregularity of metallic grains, the Fourier descriptors representation with an arc-length coordinate system is introduced for two-dimensional outline of grains. Unlike the normally used polar coordinate system, this method is applicable to any complicated shape of grain boundary. Some advantages of the present method are demonstrated for several selected Fe-Ni grains from the same specimens as those used for the magnetic and the strength measurements. Newly proposed parameters representing deviations from circular and elliptical shapes are shown to distinguish different complex outlines of Fe-Ni grains.