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The Archaean Karelia Province (3.5 –2.66 Ga) is divided into several subprovinces on the basis of lithological, structural, metamorphic and geochronological differences between them. These subprovinces are mostly formed of gneissic granitoids. Neoarchaean rocks dominate, since Palaeoarchaean and Mesoarchaean granitoids (>2.9 Ga) are only locally present in the western and northern parts of the province. Neoarchaean accretion of exotic terranes at c. 2.83–2.75 Ga and subsequent collisional crustal stacking at around 2.73–2.68 Ga may have been the mechanism that generated the present structure of the Karelia Province.
The granitoid rocks in the Karelia Province can be classified, based on their major and trace element compositions and age, into four main groups, which are the TTG (tonalite-trondhjemite-granodiorite), sanukitoid, younger granitoids (quartz diorites and quartz syenites) and leucogranite/granodiorite groups. The TTGs have a large age span from c. 3.50 to 2.73 Ga. They are plutonic rocks that appear to represent a continuous compositional series with high Na2O content. Sanukitoids have striking high Ni–Cr and Ba–Sr signature, low Na2O/K2O ratio and uniform HREE pattern. Additionally, sanukitoids have a uniform age distribution of 2.74–2.72 and 2.72–2.70 Ga throughout the province. The heterogenous younger granitoids group age is c. 2.70 Ga, it represents the youngest fractionated juvenile Archaean magmatism. The leucogranite/granodiorite group is c. 2.71-2.66 Ga old, it represents crustal melting in Neoarchaean collisional events.
The greensotone belts (mainly composed mafic volcanics and minor sedimentary sequences) typically form N-S trending synclinoriums in Karelia Province. Geochronological data obtained for volcanic rocks in the Archaean indicate distinct age groups for some of the belts: 2.94, 2.88–2.87, 2.84–2.80 Ga, 2.75 Ga, and deformed quartzite contains detrital zircon as young as 2.70 Ga. In the western Karelia subprovince greenstone belts ultamafic komatiites show an affinity to plateau basalts, and seem to derive from a slightly depleted primitive mantle-type source. In the Central Karelia subprovince greenstone belt komatiites have highly fractionated, LREE-enriched patterns that indicate extensive interaction with the associated felsic volcanics. The geochemical data suggest that the greenstone belts store a long-lived (>200 Ma) fragmentary record of geological evolution, most prominently a rift enviroment. The sediments in the paragneiss belts within TTG complexes were deposited ca. 2.72 Ga ago in back-arc environment.
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