고자기학(古磁氣學)의 방법(方法) (I)

Methods in Palaeomagnetism (I)

For the discussion of palaeogeomagnetic field direction and the movement and rotation of geotectonic blocks it is prerequisite to eliminate the secondary remanent magnetization component out of the NRM vector of given rock samples. Among various techniques alternating field and thermal demagnetization methods are most easily applicable and most widely used ones. Physical principle underlying these methods is the concept of relaxation time: Either with an action of external magnetic field or with an elevated temperature relaxation time of magnetic minerals can be drastically shortened. It has been furthermore shown experimentally that the secondary remanent magnetization can be more easily demagnetized than the primary remanent magnetization. Through careful stepwise demagnetization it should also be possible to discriminate the kind of various remanent magnetizations. In addition to the introduction to the underlying physical principles and experimental results of the alternating field and thermal demagnetization this paper gives various practical tips in earring out the demagnetization experiments. Each alternating field and thermal demagnetization instrumentation which is easily adaptable to domestic palaeomagnetic laboratories is also introduced. This paper provides a compact and practical introduction to the methods in palaeomagnetism and would be of interest to present workers and to those who want to embark on research in this field.