Stages of the Epigenetic Alteration of Upper Precambrian Rocks from the Central East European Platform: Evidence from Rb-Sr and K-Ar Isotope-Geochemical Investigations

摘要

Results of K-Ar measurements in Upper Vendian-Lower Cambrian clayey rocks drilled in the Gavrilov Yam area are considered. Combined with earlier Rb-Sr measurements, they suggest that the examined rocks experienced several stages of epigenetic alteration. One of these stages registered by Rb-Sr and K-Ar geochronometers is related to events that occurred 650 +- 50 Ma ago. Another stage (390 Ma) registered only by the Rb-Sr geochronometer was related to Hercynian activation in the East European Platform. Probable causes responsible for different behaviors of Rb-Sr and K-Ar systems during the epigenetic rock transformation are discussed. The measured age exceeds the value obtained for the same rocks by stratigraphic methods.