Z.V. Krasnozhina. GEODYNAMIC EVOLUTION OF THE KARADAG VOLCANO GROUP

https://doi.org/10.15407/gpimo2019.03.073

Z.V. Krasnozhina
GEODYNAMIC EVOLUTION OF THE KARADAG VOLCANO GROUP
Petrological and isotope geochemical studies of volcanic rocks of the Crimean paleoarc (in the ground part and the Black sea), including data from the Nd-Sr isotope together with the set of informative ratios TR, REE elements indicators of geotectonic positions allow us to consider products of arc volcanism, as relics of a different age of fragments of island arcs of the Paleo-Neo-Tethys, overlap during the Alpine orogeny, in particular, we identified examples of «back arc» volcanism of Paleo-Tethys in the composition of the volcanic rocks of the Karadag volcano group. The totality of the information received, including the ratio of TR, REE elements indicators of geotectonic positions allows to identify the basalts of the lower series of the first phase of Karadag volcanism as products «back arc» volcanism, or residual arc Paleo-Tethys (196¸4 Ma, K/Ar), characteristics of the source magma which is comparable to the source of MORB basalts in the Nb/Yb — 5, Ba/Yb — 12; 143Nd/144Nd — 0,5128; 87Sr/86Sr — 0,7039). The volcanic rocks of the later stages of the eruptions with a high probability are products of different depts and depletion magmatic sources at successive stages of the evolution of the island arc system of the Meso-Tethys with multiscale contribution of the subduction component (trachyliparites stage 2 — 150¸5 million (K/Ar), Nb/Yb — 0,8, Ba/Yb — 98; 143Nd/144Nd — 0,5126; 87Sr/86Sr — 0,7094; Kainotype dacites 3 phase (74¸16 Ma, K/Ar); Nb/Yb — 1,15; 143Nd/144Nd — 0,5127, 87Sr/86Sr — 0,7049, Ba/Yb — 60,9. Rocks of all stages of the volcanism mainly relate to tholeiite series of differentiation, andesite dacites, rhyolites final of the second stage to the limestone-alkaline series. Isotope mineralogical and geochemical characteristics of volcanic rocks of the central part of the arc (Muholatka — Iphigenia): TiO2 < 0,6 wt. %. MgO > 8 wt. %, Ba/Yb > 400 etc., confirm the assumption of a depleted magma source in the front arc of «fore arc».
Keywords: Tethys, Karadag volcanic group, isotope geochemical indicators, «back arc», Nb/Yb, Nd-Sr, geodynamic evolution.

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