自然残留磁気方向の解釈について

その他

For about twenty years many workers (Blackett et al, 1960 ; Irving, 1964 ; McElhinny, 1973) have deduced from measurements of the direction of natural remanent magnetization in rocks that continental land masses have moved relative to each other Particularly the applications of paleomagnetism to structural problems in geology and geophysics are accepted. They cover a wide field in geophysics and geology. The basic assumptions for these applications are that the remanent magnetization in rocks provides the direction of the geomagnetic field at the time of formation of the rock and that the geomagnetic field has been the field of a geocentric axial dipole. In the case of the applications of paleomagnetism, many workers mainly drrect their attention to deflection in the direction of remanent vector. It is suggested that the deflection in declination of the remanent vector is due to a rotational movement of rocks sampled about one vertical axis. From measured inclination of samples we can estimate an ancient latitude, and then we can trace a drift of land mass of the region sampled from the difference between the present and the ancient latitude, if any. In this case it is assumed that there is no stretching, folding, or distortion of any kind within a given block or land mass. The land masses or rock bodies are generally deformed for long period since the formation. However, some small intrusive rocks can be regarded as a rigid body for tectonic movements from paleomagnetic observations for various granitic masses.
In this paper a possibility of tilting of a block or land mass will be derived from paleomagnetic observations for small intrusive rocks on the basis of some assumptions of paleomagnetism and the principle of minimum rotational movement of rocks.