Russian Journal of Earth Sciences
Vol. 4, No. 2, April 2002
Petrology and Geochemistry of Rocks from the
Basement of the Pechenga Paleorift
V. R. Vetrin, O. M. Turkina, and J. Ludden
Abstract
The basement of the Early Proterozoic Pechenga paleorift was penetrated by
the Kola Superdeep Borehole over a depth interval of 6842-12261 m. The principal
types of basement rocks are gneisses of trondhjemite-tonalite composition in association
with amphibolites, gneisses containing aluminous minerals, and banded iron formation
(BIF). It was demonstrated that the paleorift basement and rock associations exposed at
the surface in the northwestern part of the Kola-Norwegian block are of similar age,
composition of their protoliths, and correspond to the main types of
sedimentary-volcanic and plutonic rocks of the Archean granite-greenstone terrane, which was
broken up into separate segments in the Early Proterozoic. Rocks of the Pechenga
Archean basement were affected by Proterozoic magmatism and metasomatism related to
the rift development. The most intense Proterozoic processes in the Pechenga basement
and its nearest surroundings were intrusion of numerous mafic-ultramafic bodies,
retrograde metamorphism to the medium- low-temperature amphibolite and epidote
amphibolite facies, synmetamorphic migmatization, and emplacement of postkinematic
granite dikes. Most Proterozoic processes were determined to have been related to mantle
sources. The overall amounts of Proterozoic material introduced into the Archean rocks
penetrated by the lowermost part of the borehole plus the remobilized Archean crustal
material were estimated at 
30%
(12-15% amphibolites, ~3% granite veins, and
~15% migmatized rocks).