International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

Sr AND Nd ISOTOPE GEOCHEMISTRY OF HERCYNIAN GRANITIC ROCKS FROM THE WESTERN CARPATHIANS — IMPLICATIONS FOR GRANITE GENESIS AND CRUSTAL EVOLUTION

Pages: 477 - 487

Authors: MILAN KOHUT, VICTOR P. KOVACH, ALEXANDER B. KOTOV, EKATHERINA B. SALNIKOVA, VALERIY M. SAVATENKOV

Abstract: Combined Sr-Nd isotopic study of the Hercynian granitoid rocks from the Western Carpathians has been carried out on whole rock (WR) samples from typical representatives of each granitic body in the Carpathians. The results presented here reveal the dominance of heterogeneous crustal sources for the majority of the studied granitic rocks, which have a neodymium crustal index NCI = 0.4–1 (majority 0.6–0.8). Initial isotopic data 87Sr/86Sr(350) = 0.7053–0.7078 (ΕSr(350) = 16.7-52.6) and ΕNd(350) = -0.6 to -6.9 preclude a simple mantle and/or crustal origin for most of the West-Carpathian granites and suggest more complex sources, such as an enriched source in the subcontinental lithosphere, or amphibolitic lower crust, with crustal-sedimentary addition. We cannot exclude, from the presented data, a hypothetical depleted mantle source, at least as heat flux during crustal anatexis processes. Apparent crustal residence ages, indicated by Nd model age — t(DM2st) = 1.1 ~ 1.6 Ga, are comparable with other segments of the European Hercynian belt. Petrographically, these granites are representative of common crustal anatectic rocks with magmatic muscovite, however, their isotopic signature reflects an I-type granitic character, usually related to subduction processes at active continental margins. Recent metamorphic, sedimentary and/or structural knowledge from the Hercynian basement of the Western Carpathians suggests a continental collisional, rather than a volcanic arc setting. The West-Carpathian granitic rocks were generated by partial melting of mainly crustal Proterozoic material during subduction-collisional processes of the Hercynian orogeny.

Keywords: Western Carpathians, granitoid rocks, Rb-Sr, Sm-Nd, isotope geochemistry, granite genesis, crustal evolution

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