Abstract
The paper reports the isotope-geochronological and petrological-geochemical studies of the Pliocene moderately-acid volcanism of the Akhalkalaki Plateau in the central part of the Lesser Caucasus (Javakheti highland, Georgia). K-Ar dating showed that young dacitic lavas and pyroclastic rocks were formed in the mid-Pliocene (3.28 ± 0.10 Ma) in relation with the explosive–effusive eruptions of small composite volcanic cones and formation of minor extrusive domes confined mainly to the eastern margin of the region. Isotope-geochronological data in the combination with results of structural drilling indicate that the considered short-term pulse of the volcanic activity occurred during a short gap between two phases of the Pliocene–Early Pleistocene mafic magmatism widespread within the Akhalkalaki plateau. The studied Pliocene dacites were erupted at the post-collisional stage of the evolution of the Lesser Caucasus, but bear petrological-geochemical affinity of adakitic series. They are characterized by the steady presence of amphibole phenocrysts, the elevated contents of Sr, Ba, LILE and the lowered contents of Y, Nb, Ta, and HREE, and have depleted Sr isotopic composition (87Sr/86Sr < 0.7045). Analysis of petrogenetic models earlier proposed to explain the generation of adakite-like magmas in the modern collision zones showed that the origin of the Pliocene dacitic lavas of the Akhlkalaki plateau is best described by the crystallization differentiation of water-saturated calc-alkaline basaltic melts with removal of common mafic rock-forming minerals (first of all, amphibole and pyroxene) and accessory phases (apatite, titanite, Ti-magnetite) as cumulus minerals. Crustal assimilation of evolved magmas only insignificantly contributed to the petrogenesis of the dacites.
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Coordinates of sampling localities, name and main petrographic characteristics of rocks are given in ESM_1.pdf (Suppl. 1) for English on-line version on site http://link.springer.com/
Results of chemical analyses of the studied magmatic rocks of the Akhalkalaki plateau (rock-forming oxides and some trace elements) obtained by XRF method are given in ESM_2.pdf (Suppl. 2) to the English on-line version on site http:// link.springer.com/
Results of chemical analysis of the studied magmatic rocks of the Akhalkalaki plateau (trace elements) obtained by ICP-MS are given in ESM_3.pdf (Suppl. 3) to the English online version of the paper on site http://link.springer.com/
Photos of some volcanic rocks studied in this work are given in ESM_4.pdf (Suppl. 4) to English online version of the paper on site http://link.springer.com/
Typical textures of the studied young volcanic rocks are shown in the microimages of polished thin sections in ESM_5.pdf (Suppl. 5) to the English online version on site http:// link.springer.com/
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Lebedev, V.A., Vashakidze, G.T., Parfenov, A.V. et al. The Origin of Adakite-Like Magmas in the Modern Continental Collision Zone: Evidence from Pliocene Dacitic Volcanism of the Akhalkalaki Lava Plateau (Javakheti Highland, Lesser Caucasus). Petrology 27, 307–327 (2019). https://doi.org/10.1134/S0869591119030056
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DOI: https://doi.org/10.1134/S0869591119030056