Magnetic analysis of Antactic ordinary chondrites and achondrites on the basis of a magnetic binary system model

• Main Authors: Takesi Nagata, Minoru Funaki
• Format: Report
• Language: English
• Published: National Institute of Polar Research 1989
• Subjects: Curie Point; The Hump; Antarc*; Antarctica
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=4493; http://id.nii.ac.jp/1291/00004493/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=4493&item_no=1&attribute_id=18&file_no=1

Magnetic hysteresis cycles of 9 ordinary chondrites and 10 achondrites, collected mainly from Antarctica, are analyzed on the basis of a newly proposed model of a non-interactive magnetic binary system, by taking into account their thermomagnetic characteristics for identifying ferromagnetic phases involved. All the chondrites and achondrites examined consist of a high-coercivity (a) component and a low-coercivity (b) component. In ordinary chondrites, the (a) component is often identified to be tetrataenite (tetragonal-ordered crystal of FeNi) having an apparent coercive force H^<(a)>_C≳10^3 Oe (TT-type phase), while in other chondrites the (a) component comprises fine grains of shape-anisotropic single-domain structure (A. SD-type phase) having H^<(a)>_C=(2∿5)×10^2 Oe. The (b) component consists of mostly multi-domain grains of kamacite and/or taenite of H^<(b)>_C≲20 Oe. In most achondrites, the (a) component comprises A. SD-type phase of H^<(a)>_C=(2∿5)×10^2 Oe except a special case consisting of a small amount of tetrataenite. The structure of the (b) component in achondrites is the same as in ordinary chondrites. An anomalous hump-shape rise in saturation magnetization (I_s) between 330℃ and Curie point of taenite (540∿590℃) during the initial heating process is found in diogenites and a eucrite. The thermomagnetic hump is considered here to be due to an increase of A. SD-type phase of taenite associated with a relatively smaller increase of the (b) component multi-domain phase. However, a possible metallographical interpretation of the hump phenomenon has not yet been obtained.