oa Определение мощности палеозойских отложений над импактным кратером Ritland по магнитным свойствам горных пород

A palaeomagnetic analysis of the Ritland impact structure in Ryfylke, Norway, was carried out with the purpose to date the impact. The palaeomagnetic dating was problematic, because the apparent polar wander curve for the Ediacaran and Cambrian is fragmented and some of the analysed rocks carried no detectable primary magnetisation. The analysis, however, showed a well defined secondary component which was present in all rocks investigated. This secondary magnetic component is interpreted as a partial thermal remanent magnetisation. It has a direction indicating that it was imposed during the early Permian. Because there are no magmatic rocks of that age in the area, the remagnetisation is interpreted as having been caused by elevated temperatures due to burial. The magnetisation temperature can be estimated from the Neel equation describing the relation between magnetisation temperature and time and demagnetisation temperature and time. Using this equation a magnetisation temperature of 150ºC is estimated if the magnetisation of the rocks occurred during 10 million years. A magnetisation temperature of 150ºC corresponds to a burial depth of 4‐5 km if a palaeogeothermal gradient of 25‐30ºC is assumed.