THE PRE-VENDIAN (640-610 MA) GRANITE MAGMATISM IN THE CENTRAL TAIMYR FOLD BELT: THE FINAL STAGE OF THE NEOPROTEROZOIC EVOLUTION OF THE SIBERIAN PALEOCONTINENT ACTIVE MARGIN

Abstract

Eastern part of the Central Taimyr belt is composed of Precambrian rocks penetrated by granites of the Snezhnaya complex (845-825 million years) and later overlain by mid-Neoproterozoic sinpostorogenic sedimentary deposits of the Stanovaya-Kolosova Group. Two competing concepts on the Precambrian history of the belt are discussed. The first suggests that by the middle of the Neoproterozoic amalgamation of various terrains formed the Central Taimyr microcontinent, which afterwards collided with Siberia in Vendian. 2) According to the second point of view, which is shared by the authors of this article, the belt was part of the Siberian craton from at least the Mesoproterozoic, and there is no suture that would separate it from the South Taimyr belt. To our surprise, during the field work in the South-Eastern part of the Central Taimyr belt near the proposed “Vendian sutura”, assumed by the first concept, we found a granite pluton (Pregradnaya massif) intruding clastic rocks of Stanovaya-Kolosova Group. Such setting is quite uncommon for the belt and contradicted to publications, describing the mentioned clastic rocks to overlay the granites and contain their debris. Dating of the pluton confirmed the field observations its SRIMP zircon age has proved to be 609±2 Ma, an unusually young for this region. The pluton is located in a wide deformation zone separating the Precambrian rocks (to the northwest) and the Paleozoic deposits (to the southeast). Two minor bodies of similar porphyritic granite were found in the same zone further to the southwest, and it seemed logical to assume that a chain of Vendian granites marks boundary deformation zone. However, their dating (843±6 и 840±5 Ma) showed that they belong to Snezhnaya complex. In this paper, we discuss two Neoproterozoic magmatic ‘flare-ups’ in the Central Taimyr Belt, which are dated at 845-825 and 640-610 Ma. Both ‘flare-ups’ are evidenced by K-rich peraluminous granite batholiths intruded the upper crust. It is most probable that each flare-up was related to a collision event completing an independent cycle in the evolution of the active margin of the Siberian paleocontinent.