Tuffisite rocks in the basement of the early proterozoic Pechenga structure

The problematical Early Proterozoic fluidizite-explosive tuffisites have been considered in the Televi Sedimentary Fm of the Northern Pechenga volcano-sedimentary complex. Fluidizite-explosive "pseudoconglomerates" occur as irregular clastic rocks, without evidence of sorting by size and shape. Clastic fragments are represented by plagiogranites, granodiorites, diorites and quartz pebbles. Fragments have an angular or subround shape. There are a number of the plastic picrobasaltic lava fragments that were deformed by hard granitic clasts. This fact indicates high-temperature conditions of tuffisite-forming process. These conditions are also confirmed by a fact of volumetric decompaction processes in tuffisite fragments. Quartz grains from the granitic clasts are partly replaced by diaplectic glass. Such decompaction processes and quartz transformations are typical of latest diamond-bearing tuffisites of Polar Ural and Timan Area. The matrix of the Pechenga tuffisites is enriched in such compatible elements as Ni, V, Cr, and Со, that is typical for tuffisitic rocks and for endogenic "pseudoastroblems". Rb-Sr isochrone with the age of 2595 ± 79 Ma has been received for these rocks.