一个变泥质岩包体样品的系统热磁试验及其矿物学意义

利用一件采自河北汉诺坝周坝地区变泥质岩包体样品，结合系统的低温和高温磁性测量结果，探讨了应用热磁实验鉴别样品中所含原生磁性矿物的多解性问题. 结果表明， 饱和等温剩余磁化强度（SIRM）在室温～250℃以及280℃～380℃的降低分别由高钛钛磁铁矿的剩磁解阻过程（一种物理过程）以及由磁赤铁矿转换成赤铁矿（一种矿物相变）引起.样品在500℃以后磁化率的升高则是由磁铁矿从钛磁赤铁矿中出溶所致.因此，κ T（即磁化率随温度变化）曲线中呈现约580℃居里点是由加热过程中次生的磁铁矿引起，而并非代表原始（即加热前）样品中的磁铁矿成分.

Determination of primary magnetic minerals of a weathered metapelite xenolith from Zhouba region, North China, by combining thermomagnetic runs and low-temperature measurements

We have combined low and high temperature measurements for identifying possible mineral transformations (e.g., maghemite to hematite, titanomaghemite to magnetite) in thermomagnetic runs (magnetic susceptibility vs. temperature) for a weathered metapelite xenolith sample from Zhouba, North China. The results show that lab induced saturation isothermal remanence magnetization (SIRM) changes observed between room temperatures and 250℃, and between 280 and 380℃ are caused by the remanence unblocking of titanomagnetite (a physical process) and the inversion from maghemite to hematite (a mineralogical phase transformation), respectively. Furthermore, the significant increase of susceptibility after 500℃ is interpreted as the mineral exsolution of magnetite from titanomaghemite. Thus, the magnetite like Curie temperature revealed by κ T curves is caused by the neoformation of magnetite.