Magnetic properties of high petrologic grade L-LL chondrites: Tenham,Tuxtuac,Willard and Forrest(b)

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Temperature dependence of the hysteresis parameters (saturation magnetization, Js; saturation remanent magnetization, Jr; coercivity, Hc; and initial susceptibility, Xi) were examined from room temperature to 780℃ for Tenham (L6), Tuxtuac (LL5), Willard (L6) and Forrest (b) (L6) chondrites. Their main magnetic minerals were determined from the analyses of transition temperatures (Θ_<Js>, Θ_<Hc>, Θ_<Xi>). The NRM characteristics of these chondrites were measured and are discussed on the basis of magnetic properties. The main magnetic minerals of the Tenham chondrite are taenite (γ-(Fe, Ni)) with 54 at % Ni and kamacite (α-(Fe, Ni)) with 7 at % Ni, and the main NRM carrier is taenite. Tenham has a stable NRM. Tuxtuac mainly contains tetrataenite and taenite (the ratio tetrataenite : taenite is 15 : 85,T. NAGATA et al., Mem. Natl Inst. Polar Res., Spec. Issue, 41,364,1986) and they both contribute to NRM. The NRM of Tuxtuac is rather unstable magnetically. The main magnetic minerals of the Willard chondrite are the same as those of Tenham, i. e. taenite with 54 at % Ni and kamacite with 7 at % Ni. The main NRM carrier is taenite. Willard has an unstable NRM. Forrest is suggested to have experienced some alteration, on the basis of the analysis of the Js-T curve, and may have acquired a secondary NRM of probable terrestrial origin.
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