Magnetic analysis of Antarctic chondrites on the basis of a magnetic binary system model

• Main Author: Takesi Nagata
• Format: Report
• Language: English
• Published: National Institute of Polar Research 1988
• Subjects: Antarctic; Antarc*
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=4461; http://id.nii.ac.jp/1291/00004461/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=4461&item_no=1&attribute_id=18&file_no=1

Ordinary chondrites often have extremely large values of their remanence coercive force (H_<RC>) while their coercive force (H_C) is not particularly large, H_<RC>/H_C often amounting to a magnitude larger than 30. Since H_<RC>/H_C of ferromagnetic materials is generally smaller than 5,the observed large values of chondrites are considered anomalous. A magnetic binary system model consisting of (a)-component having large H_C and H_<RC> values and (b)-component having small H_C and H_<RC> values can approximates the anomalously large value of H_<RC>/H_C. Using the magnetic binary system model, Antarctic chondrites having anomalously large values of H_<RC>/H_C are analyzed; metallic constituents in these chondrites are decomposed into (a)-component with H_C≳1000Oe and (b)-component with H_C≲30Oe. Interest from a viewpoint of meteoritics may be concerned with following results of the analysis. (i) With the aid of thermomagnetic analysis and other methods, the high coercivity component (a) is identified to tetrataenite which has an extremely large value of H_C, while the absolute majority of (b)-component comprises relatively large grains of kamacite of multi-domain structure. (ii) Metallic fine grains in both chondrules and matrix of ALH-769 (L6) chondrite are composed of statistically same tetrataenite and kamacite. This result suggests that both chondrules and matrix were extremely slowly cooled down together through 320℃ in the final process of the thermal history of this chondrite.