[S-EM13] Geomagnetism, paleomagnetism and rock magnetism

[SEM13-03] A hydrothermal experiment for pedogenic magnetite/hematite formation with Chinese loess-paleosol samples

*Masayuki Hyodo¹, Yusuke Seto², Balazs Bradak³ (1.Research Center for Inland Seas, Kobe University, 2.Department of Geosciences, Osaka Metropolitan University, 3.Faculty of Oceanology, Kobe University)

Keywords:pedogenic magnetite/hematite, hydrothermal experiment, magnetic susceptibility, super paramagnetic

Soils are formed by aqueous alterations of clastics produced by physical and chemical weathering of rocks on the earth’s surface. Soil formation is advanced under moist conditions, and thus reflects precipitation. Pedogenesis accompanies the formation of magnetic minerals that cause magnetic susceptibility enhancement of paleosols. Therefore, magnetic susceptibility is often used as proxies of pedogenesis and paleoprecipitation. In spite of the actual profits, we do not understand how magnetic minerals are formed in soils. To solve this problem, we carried out hydrothermal (HT) experiments to produce pedogenic magnetic minerals with closed-type pressurized reactor cases, using loess-paleosol samples from the Chinese Loess Plateau. The experiments were conducted with various heating times at temperatures of 200 and 170 degrees C. All the samples show magnetic susceptibility increases after HT heating. Hysteresis measurements and IRM acquisition experiments reveal the followings. (1) Large quantities of super-paramagnetic (SP) magnetite and hematite particles are formed. During post-HT experiment natural drying of samples at room temperature, (2) pre-existing magnetite particles increase in size, and (3) single domain (SD)/ Vortex state size hematites and magnetites are newly formed from SP size hematites/magnetites. (4) These magnetic changes cause complex temporal variations in magnetic susceptibility for HT heated samples.