THE VENDIAN - CAMBRIAN BOUNDARY: RB-SR ISOCHRON AGE OF THE FINAL EVENT OF ALKALINE ULTRABASIC MAGMATISM IN THE NORTHEASTERN SAYAN REGION

Abstract

The Vendian–Cambrian boundary is one of the most important geological milestones in the Earth’s evolution. It is suggested that the short-living Pannotia supercontinent was breaking out at that time as a result of vigorous global tectonothremal activity. Magmatism of this age was spectacular at the periphery of the West African Craton, which played the role of thermal insulation cover in the Late Precambrian. The heat release as a consequence of magmatic activity induced the melting of the polar ice sheet, eustatic sea-level rise, and greenhouse and other effects favorable for the bloom of living organisms [1]. Study of Late Precambrian magmatic events at margins of other cratons are required to substantiate this hypothesis. In this work, we report the results of Rb–Sr isotopic dating of the late Vendian Zima alkaline ultrabasic igneous rock complex from the Sayan uplift of the Siberian Craton basement.