Age Measurements on Rocks from the Finnish Precambrian

Abstract

New mineral age measurements are reported from several subdivisions of the Finnish Precambrian. Samples of zircon, feldspar, and muscovite collected from the gneissose pre-Karelian basement area in eastern Finland indicate an age of about 2,700 million years for these rocks. In contrast, biotite ages from the same rocks agree at 1,800 million years, presumably representing the effect of the orogeny at this time. the correlation of these rocks with the pre-Karelian basement to the east, while again the biotite ages represent the time of the 1,800-million-year orogeny. These results are very analogous to data previously reported for mantled gneiss domes near Baltimore, Maryland. Additional measurements on the younger Precambrian rocks of Finland confirm earlier data indicating an age of around 1,800 million years for plutonic rocks associated with both the Svecofennian and Karelian orogenic belts.