About a possible second source of trap magmatism in the east of the Siberian craton

Abstract

There was made a comparison of trap formation of two major tectonic structures of the eastern part of the Siberian craton - north-east of the Tunguska syncline and Olenek uplift. Using the analysis of geological data and isotopic age determination by the methods of 40Ar/39Ar and U-Pb (also outside the researching area), we can conclude, that the traps of the Tunguska syneclise are 264-240 million years Permo-Triassic age, at the same time, the age of the traps of the Olenek uplift defined as Lower Triassic. The traps of the Tunguska syneclise were formed in three independent intrusion phases, each has its petrochemical specifics, but at the Olenek uplift, there was a single impulse that formed the rocks of the same type, with a well-defined pre-chamber stage of the melt crystallization. The magma that formed the dolerites of the Olenek uplift was more magnesian. The REE distribution patterns for the traps of the Olenek uplift are steeper (La/Ybn=2.4-2.8) in comparison with the Tunguska syneclise traps, the total amount of REE (g/t) in them is within 58-63. A well-defined Sr maximum, promoted by the presence of the early-formed basic plagioclase, is mostly shown in the Olenek uplift traps. In the Nb/Th-Zr/Nb and Nb/Y-Zr/Y diagrams of chemical behavior to incompatible elements, dolerites of the Olenek uplift form composition fields, which are isolated from the Tunguska syneclise traps, thus showing their specific nature. So this information gives us the right to talk about two different sources for the trap forming of the Tunguska syneclise and the Olenek uplift. They resulted from independent plume-induced magmatic events.