THE SM-ND ISOTOPIC AGE AND SOURCE OF COMAGMATIC ALKALINE MAFIC ROCKS AND CARBONATITES OF KUZNETSK ALATAU

Abstract

Carbonatite and alkaline magmatism repeatedly occurred within the southwestern Siberian Platform and its folded surrounding during Late Riphean, Early-Middle Paleozoic, and Late Mesozoic. The least determined is the timing of Paleozoic associations of alkaline rocks and carbonatites in the western Altai-Sayan zone. Their formation is generally attributed to the Devonian rifting within consolidated foldbelts at the craton margin. Up to the present, such viewpoints were based on controversial geological relations and widely varying K-Ar datings. The revision of this concept was made possible by recent evidence of development and long-term existence of mantle plume, which affected the lithosphere from Late Cambrian to the end of Devonian [1]. The correction and refinement of main stages of the magmatic activity closely related to plume evolution will be one of the important directions of subsequent investigations. Therefore, our work presents new isotopic-geochronological data on carbonatites and comagmatic alkaline mafic rocks of the Verkhnepetropavlovsk Pluton on the northern slope of Kuznetsk Alatau, which were previously considered as Devonian formations. These data suggest Late Cambrian-Early Ordovician age of these rocks and their possible formation at the initial stage of plume activity.