Study of thermomagnetic identification of greigite as an indispensable carrier to natural remanent magnetization of sediments

这项研究的主要目的是阐明云母的热磁性质，云母是一种在各种类型的沉积物中普遍存在的次要但不可或缺的磁性矿物。在以往的大部分工作中，灰岩的居里温度都被报道为320摄氏度。然而，一些含有云母的沉积物显示出接近400摄氏度的稳定剩磁。为了解决这种不一致性，我们对台湾南部二仁池剖面的天然云母样品进行了岩石磁学和X射线衍射(X射线衍射)研究。X射线衍射结果表明，云母在加热到340摄氏度后存活下来，但在此温度以上很难检测到磁性。我们还在氦气气氛中应用了高温X射线衍射法。在380℃以上的加热过程中，我们还发现了磁黄铁矿、黄铁矿和铁铁矿的新形成，在380℃以上还观察到了赤铁矿。这些结果与一些含灰云母沉积物在400℃加热后可以保持剩余磁化的事实相一致。然而，一些新形成的矿物可以显示出从原始磁性矿物继承而来的磁化。我们现在正在考虑继续对这个问题进行进一步的研究，因为我们还发现我们的结果强烈依赖于样品的纯度。有必要通过使用几个不同的样品来检查结果的重复性。

The main target of the research is to elucidate thermomagnetic property of greigite which is generally found as a minor, but indispensable magnetic mineral in various types of sediments. The Curie temperature of greigite has been reported as 320 degrees C in most of the previous works. However some of the greigite-bearing sediments show stable remanence close to 400 degrees C. To solve this inconsistency, we conducted rock magnetic and X-ray diffraction (XRD) studies using natural greigite sample form Erhjen-chi section, southern Taiwan.XRD results show that greigite has survived by heating up to 340 degrees C, but difficult to detect magnetically above that temperature. We also applied a high-temperature XRD method in helium atmosphere. The existence of greigite was confirmed during the heating up to 380 degrees C. We also found neo-formation of pyrrhotite, pyrite, and marcasite by the heating above 340 degrees C. Hematite was also observed above 380 C. These results are consistent with the fact that some of the greigite-bearing sediments can hold remanent magnetization after the heating up to 400 degrees C. Some of neo-formed minerals could show the magnetization inherited from the original magnetic minerals, however.We are now thinking to continue further investigation on this topic, because we also found that our result was strongly dependent upon the purity of the sample. It is necessary to check reproducibility of the results by using several different samples.