Title

N.A. ARESTOVA, V.P. CHEKULAEV, G.A. KUCHEROVSKIY, YU.S. EGOROVA (IPGG RAS), S.G. SKUBLOV (IPGG RAS, SPMU)

About the conforming of geological data and the results of zircon U-­Pb dating of Archaean rocks on the example of the Karelian province of the Baltic Shield

We studied the zircons of the Paleomesoarchaean and Neoarchaean rock complexes of the Vodlozero domain of the Karelian province of the Baltic Shield. The morphology, the internal structure of zircons, the content of REE, Li, Sr, Ba, Ti, Nb, Hf, Th, and U were studied. Zircons of ancent tonalites (<3.1 Ga) preserve magmatic REE patterns (Yb/La 5500–3000, Ce/Ce* 12–17, Eu/Eu* 03–04). They are not formed during the crystallization of younger rocks, but are present as xenogenics alongside with their own zircons in the trondhjemite dykes (2.9 Ga), in gabbro (3.02 Ga) and andesites dykes (2.92 Ga) that cut through the basement tonalites. Basites of the earlier complex (3.02 and 2.86 Ga) contain zircons without nuclei, preserve magmatic REE patterns (Yb/La 2300–800, Ce/Ce* 4–20, Eu/Eu* 0.05–0.8), and reflect the crystallization age. The concentrations of Li and U/Yb–Y correspond to zircons from continental crust. Andesites of the early dyke complex in base tonalites preserve a magmatic distribution of REE, but zircons from sills and andesite covers in greenstone structures have been changed, and their age reflect the age of metamorphism (2.84–2.86 Ga). The rocks of Neoarchaean volcano-­plutonic complex do not contain zircon, reflecting the age of their crystallization. The age of these rocks is determined by the interval between the crystallization of the basites 2 of the earlier complex (2.86 Ga) and the intrusion of the latest Neoarchaean basic dykes (2.72 Ga).
Keywords: Baltic Shield, Vodlozero domain, isotopic age of rocks, zircon, trace elements.