Paleomagnetism of the dike systems in Finland IV: Remanent magnetization of the dolerite and related dikes in the Åland archipelago

Abstract

The dikes of the area can be divided into three groups having different directions of remanent magnetization after demagnetization in the AC field. One of these groups has a direction which coincides with that measured for the Jotnian dolerites in the Satakunta and Vaasa archipelago. The direction of the second group differs but slightly from this and the third one has a reversed orientation. The age relations and the origin of the magnetization are discussed. CONTENTS Introduction 57 Samples 58 Measurements and demagnetization 59 Discussion 61

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

“…The second set of magnetic orientation coincides with that observed for the Kumlinge diabase occuring just south of the Åva area (D = 177°, I = +39°, Neuvonen and Grundström, 1969). This direction is encountered in samples from the broad diabase dike at Korsö which is an occurence very different from the Ava diabases proper (see.…”

“…Calculations are based on the mean magnetic directions measured on demagnetized samples with a95 less than 25°. The pole positions are not very far from the sites calculated for the doleritic dike rocks in western and southwestern Finland by Neuvonen (1965 and1966) and by Neuvonen and Granström (1969). The Kumlinge diabases show reversed magnetization and the precision of the determination of this pole is somewhat improved when compared with the result obtained for it earlier.…”

“…A magnetic cleaning was performed at 350-500 Oersteds peak field after runs of several pilot samples. The instrumentation used was principally the same as that of Creer (1959) and described in Neuvonen (1965). Summary and statistic of the measurements before and after demagnetization are given in Tables 1 and 2, respectively.…”

“…During the course of paleomagnetic investigations performed in Finland, the author has found (Neuvonen, 1969) that the stable magnetization of the magnetite bearing rocks seems to be limited to those in which a very fine grained ulvite-magnetite intergrowth occurs. This feature is most typical in the fast cooled volcanic and hypabyssal igneous rocks.…”

Paleo-position of the North China craton within the supercontinent Columbia: Constraints from new paleomagnetic results

“…The poles are quite similar and the Lake Ladoga pole passes both a baked contact test and a reversal test. The ∼1265 Ma was averaged with several earlier results from sills and dykes (Vaasa dolerites pole, Neuvonen, 1966;Market dolerites pole, Neuvonen and Grundström, 1969;Satakunta dolerites pole, Neuvonen, 1965) by both Buchan et al (2000) and Pesonen et al (2003) and was frequently used as a key pole. The situation for establishing the position of Siberia is more problematic.…”