The Pre-Cambrian history of Sweden

Abstract

Several difficult problems remain to be solved in the Pre-Cambrian of Sweden but in recent years progress has been made with the establishment of a time-scale. Two major phases of regional alteration, marked by extensive gneissification culminating in the formation of special granites and pegmatitic intrusion of regional extent, have been dated. In both cases temperatures were so high that argon-40 was entirely or almost entirely expelled. The ages obtained are therefore those of the rejuvenation of the rocks. The earlier of the two phases took place 1700 m.y. to 1800 m.y. ago, marking the close of Svecofennian-Karelian time. It corresponds to the Hudsonian in Canada and the Penokean in the U.S.A. A younger phase of regional alteration, the Sveconorwegian, is dated at 950 m.y. to 1000 m.y. and took place at the end of Gothian-Dalslandian time. This corresponds to the Grenville in both Canada and the U.S.A. The high-grade gneisses of south-western Sweden are bounded to the east by a zone of marked schistosity. Age-determinations from this zone have given an age of about 1200 to 1300 m.y.