Paleomagnetism of the dike systems in Finland v. remanent magnetization of the Åva intrusives

Abstract

The direction and strength of remanent magnetization were measured for different intrusive rocks of the Precambrian Åva ring intrusion. Two nearly opposite directions were revealed after demagnetization, both in agreement with earlier measurements in SW-Finland. The pole sites are compared with those measured in Sweden. The pole wandering curve and the reversal periods are considered as tools in the Precambrian stratigraphy.

Palaeomagnetism of the Rogaland precambrian (southwestern Norway)

“…Other Precambrian pole positions of the Baltic Shield have been reported by CORNWELL (1968) from northern Sweden, by NEUVONEN (1965NEUVONEN ( , 1966NEUVONEN ( , 1970 and by NEUVONEN and GRUNDSTROM (1969) from Finland. These poles, which are given in table 2 and plotted in fig.…”

“…The ages of about 1550 × 10 6 y may be explained by an initial Ar content or an Ar enrichment of the dikes during the intrusion in an old alkali-rich rock. The high magnetic stability of the Swedish hyperite dikes and the existence of two polarities do not point to a remagnetization of these dikes, as has been suggested by NEUVONEN (1970).…”

Remanent magnetization of the Jotnian sandstone in Satakunta, SW-Finland

“…2) lies close to the poles of the Vaasa and Satakunta dolerites (Neuvonen, 1970). This could mean that the age of the sandstone is also near to (but a little older than) that of the dolerites.…”

“…According to the present author, all the dating methods are affected by the elevated temperatures prevailing in the lower levels of the crust. High temperature means an increased speed of diffusion in the rock which causes the daughter element to migrate out of a radioactive mineral thus finally bringing the radiometric »clock» to a stop (Neuvonen, 1960). Each radioactive mother-daughter pair has it's own temperature and depth, the so called »zeroline», at which it is no longer able to measure age.…”

A palaeomagnetic survey of the Jotnian dolerites of central?east Sweden

“…Also, in studies of Jotnian dolerites from Finland (Neuvonen 1965(Neuvonen , 1966 the overall mean direction computed from the af cleaned directions has a steeper negative magnetic inclination than that computed from the total NRM, and reflects the removal of a similar small viscous component to that present in the Swedish dolerites.…”