Geochemical and geochronological correlation of paleoproterozoic acid volcanites and granitoides in the conjunction zone between the Karelian Craton and Belomorian mobile belt (North Karelia)

Abstract

A comparative geochemical, isotopic-geochemical, and geochronological study of Paleoproterozoic acid volcanic rocks and granitoides at the conjunction zone between the Karelian Craton and Belomorian mobile belt was carried out. Acid volcanites comprise the Ozhiyarvi suite (Sumian Superhorizon, Lower Karelian) within the Panayarvi-Vygozero belt of Karelides. In general, the Ozhiyarvi suite is composed of quartz plagioporphyrites, rhyolites, and rhyodacites of the potassium series. Granitoides compose intrusions extending as a parallel belt located northeast of the belt of Karelides. Granitoides are represented by two spatially related associations: early gabbro-diorite-granodiorite-charnockite (vichansky type) and later granosyenite-granite (Topozersky type). Acid volcanites are of Sumian age 2442 ± 17 Ma (U-Pb, SHRIMP-II). The U-Pb age values obtained for granitoides (five determinations, SHRIMP-II) are in the range of 2445 ± 17–2397 ± 30 Ma, which corresponds to the Sumian. General geochemical characteristics of granitoides and acid volcanites are the following: low Al2O3 content, variable low CaO content, higher SiO2 content, higher total alkali with a predominance of K2O over Na2O, low to moderate ferruginosity, and higher Zr, Y, Hf, and Nb contents. These rocks are characterized by a similar distribution of rare and rare earth elements with negative Eu anomaly and distinct minima of Nb, Sr, P, and Y characteristic of A-type granites. The fields of measurement points on the Nb-Y-Ce diagram and Y/Nb and Yb/Ta ratios are evidence that the studied rocks were melted from the continental crust. The studied rocks are characterized by negative ɛNd values (−1.2 to −3.8). Their model age (2.8–3.0 Ga) is much higher than the crystallization age, which may indicate that the magma source had a long geological history. According to similar geochemical peculiarities of granitoides and volcanites, as well as their convergence in space and time, one can suggest that these rocks were melted from the continental sialic crust owing to uplifting of the mantle material into the continental crust; that is, they can be considered to be products of a unified regional magmatic process.