The isotope geology of the Precambrian of the Baltic Shield

Abstract

Recent radiometric mineral dating carried out by K–Ar, Rb–Sr, and U–Th–Pb methods makes it possible to estimate the age boundaries for the main geological formations of the Baltic Shield.The relevant radiometric age zonation does not point to a zonation of continuous growth of the Baltic Shield from the center to the periphery. In its Precambrian history three main stages can be recognized. Most of this territory developed continuously from 3500 m.y. to 1650 m.y. ago. During this first, greatest period the main structural features of the Shield were formed.The following, Gothian period, corresponding to a time interval 1500–1000 m.y. was characterized by consolidation of the Shield and deposition of continental sediments. The main feature of the third, Riphean period beginning approximately at 1000 m.y. was the formation of the Sveco–Norwegian structural belt in the southwestern part of the Shield, discordant to the older formations.