Tokko section as a deeply eroded part of the Mesoarchean Tokko-Khani greenstone belt, the west Aldan shield, Siberian craton

Abstract

This paper presents new data on the Tokko section of the central part of the Olekma granite-greenstone terrain (Aldan Shield, Siberian craton). The conducted studies provide grounds to propose that the Tokko section exposes a fragment of a deeply eroded greenstone belt, similar on the evolution to the Olondo greenstone belt. In that light the Tokko section may have been merged with the Olondo fragment within a single structure of the Tokko-Khani greenstone belt.

Juvenile geochemical signatures of felsic magmatism in the Tokko segment support the idea of the existence of an oceanic basin in the central part of the Olekma granite-greenstone terrain, evolution of which could give rise to the formation of the subduction systems and generation of the new crust during the Mesoarchean. It has been established that the main volume of the Archean crust in the Tokko section was formed between 3.0 and 2.8 Ga, primarily contributed by juvenile granitoids, and subordinately by mafic magmatism. The following stage of the crust formation is recorded by bimodal magmatism at ca. 2.6 Ga, accompanied by the ascent of mafic asthenospheric magmas and intrusion of crustal granitoids. The rocks of this association, together with the contemporaneous granites from the eastern part of the Olekma granite-greenstone terrain, and anorthosites with granitoids of the Kalar, Altual’skii, and Dzheluiskii Complexes distributed within the junction zone of the Olekma granite-greenstone terrain and the Dzhugdzhur-Stanovoi fold region, may represent a part of the single Neoarchean anorthosite-mangerite-charnockite-granite magmatic province.