关键词: 泥炭, K-T曲线, 温度, 磁铁

Abstract: Sedimentary rock, some metamorphic rock, acidicrock and the sample dominated by peat or organic matter are all located in the weak magnetic measurement range. How to explain the low magnetic susceptibility in the point of magnetic mineral? As the reliable atmospheric archive of the present and past, peat sediments have high organic matter and low magnetic susceptibility, What is the dominant magnetic properties of the mineral. Whether K-T curve can help to recognize the magnetic minerals and magnetic properties in the peat, whether it also helps to understand the sources of magnetic minerals and how organic matter affects magnetic minerals under the influence of the temperature. To understand these, the paper conducted magnetic investigation to a surface peat sample on the Altay Mountains, Xinjiang Uygur Autonomous Region, China. Mainly based on the K-T curve, combined with the J-T curve, hysteresis parameter and XRD experiment, the paper made thermomagnetic  experiment to distinguish magnetic property of weak magnetic substance which contain plenty of organic matter. The heating and cooling K-T curves are reversible, indicating that crystalloid structure and magnetic domain do not change before the samples are heated to 200 ℃. The cooling lines of magnetic susceptibility all locate above the heating line after being heated to 300 ℃, 400 ℃, 500 ℃, 600 ℃ separately and the changing extent escalates, which shows that more and more magnetic minerals come into being during the heating. When being heated from 0 ℃ to the maximum temperature of 700 ℃, the most distinctive decreasing of magnetic susceptibility occurs at around 580 ℃ and then quickly decreases to 0 ℃, which indicates the presence of magnetite and it demonstrates the unblocking temperature of magnetite. During the cooling process from 700 ℃ to 500 ℃，magnetic susceptibility slowly decreases, denoting the magnetite probably transforms. For the J-T curve, when the sample starts to be heated, the magnetization slowly decreases. When being heated to around 380 ℃, the magnetization suddenly increases and arrives at its max at around 460 ℃, then it starts to decrease, the distinct turn is 580 ℃ and decreases to zero, which means that this mineral is magnetite. In Day-plot, the plotted scatter of the raw sample is mostly located in the PSD area, when being heated from 0 ℃ directly to 700 ℃，the samples are mostly located in the MD area, indicating that magnetic particulate becomes coarse during the heating, which corresponds to the magnetic domain reflected by hysteresis loops. The results of Xray diffraction show that the main mineral in original peat is quartz, albite, illite, there are also ironcontaining chlorite and magnetite. The results show that the lowcoercivity magnetite contributes most to the magnetic susceptibility. Its grain size is PSD. During the heating, the chlorite break up into new magnetite, magnetic domain transformed into MD. The gradual heating K-T curve indicates that K-T curve is an indicator to analyse the magnetic properties of the weak magnetic substance which contain mass organic matter. The type and quantity of the magnetic mineral created during the heating are not only controlled by the highest temperature, they also present diversity when the peat samples are heated to the different temperature because organic matter has reducing action to the magnetic minerals, which make the transformation, reform and the final product complicated when the samples are heated to different temperature.

Key words: peat, K-T curves(temperature dependence susceptibilities), temperature, magnetite