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Article

Geochemical, Isotopic and Petrological Constraints on the Origin and Evolution of the Recent Silicic Magmatism of the Greater Caucasus

1
Fersman Mineralogical Museum of the Russian Academy of Sciences, 119071 Moscow, Russia
2
Geological Department, Lomonosov Moscow State University, 119234 Moscow, Russia
3
Department of Earth Sciences, University of Oregon, Eugene, OR 97403, USA
4
Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry (IGEM) of the Russian Academy of Sciences, 119017 Moscow, Russia
*
Author to whom correspondence should be addressed.
Academic Editors: Sung Won Kim and Dominique Gasquet
Minerals 2022, 12(1), 105; https://doi.org/10.3390/min12010105
Received: 13 October 2021 / Revised: 5 January 2022 / Accepted: 12 January 2022 / Published: 16 January 2022
Significant volumes of rhyolites and granites of the Pliocene-Pleistocene age are exposed in the collision zone of the Greater Caucasus, Russia. The volcanic history of the region includes ignimbrites and lavas associated with the Chegem caldera (2.9 Ma) and Elbrus volcano (1.98 and 0.7 Ma) and rhyolitic necks and granites in Tyrnyauz (1.98 Ma). They are characterized by a similar bulk and mineral composition and close ratios of incompatible elements, which indicates their related origin. The 1.98 Ma Elbrus ignimbrites, compared to the 2.9 Ma Chegem ignimbrites, have elevated concentrations of both compatible (Cr, Sr, Ca, Ni) and incompatible elements (Cs, Rb, U). We argue that the Elbrus ignimbrites were produced from magma geochemically similar to Chegem rhyolites through fractionation crystallization coupled with the assimilation of crustal material. The 1.98 Ma Eldjuta granites of Tyrnyauz and early ignimbrites of the Elbrus region (1.98 Ma) are temporally coeval, similar mineralogically, and have comparable major and trace element composition, which indicates that the Elbrus ignimbrites probably erupted from the area of modern Tyrnyauz; the Eldjurta granite could represent a plutonic reservoir that fed this eruption. Late ignimbrites of Elbrus (0.7 Ma) and subsequent lavas demonstrate progressively more mafic mineral assemblage and bulk rock composition in comparison with rhyolites. This indicates their origin in response to the mixing of rhyolites with magmas of a more basic composition at the late stage of magma system development. The composition of these basic magmas may be close to the basaltic trachyandesite, the flows exposed along the periphery of the Elbrus volcano. All studied young volcanic rocks of the Greater Caucasus are characterized by depletion in HSFE and enrichment in LILE, Li, and Pb, which emphasizes the close relationship of young silicic magmatism with magmas of suprasubduction geochemical affinity. An important geochemical feature is the enrichment of U up to 8 ppm and Th up to 35 ppm. The trace element composition of the rocks indicates that the original rhyolitic magma of Chegem ignimbrites caldera was formed at >80%–90% fractionation of calc-alkaline arc basalts with increased alkalinity. This observation, in addition to published data for isotopic composition (O-Hf-Sr) of the same units, shows that the crustal isotopic signatures of silicic volcanics may arise due to the subduction-induced fertilization of peridotites producing parental basaltic magmas before a delamination episode reactivated the melting of the former mantle and the lower crust. View Full-Text
Keywords: rhyolite; ignimbrite; Elbrus; Chegem caldera; collisional magmatism rhyolite; ignimbrite; Elbrus; Chegem caldera; collisional magmatism
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MDPI and ACS Style

Shcherbakov, V.; Bindeman, I.; Gazeev, V. Geochemical, Isotopic and Petrological Constraints on the Origin and Evolution of the Recent Silicic Magmatism of the Greater Caucasus. Minerals 2022, 12, 105. https://doi.org/10.3390/min12010105

AMA Style

Shcherbakov V, Bindeman I, Gazeev V. Geochemical, Isotopic and Petrological Constraints on the Origin and Evolution of the Recent Silicic Magmatism of the Greater Caucasus. Minerals. 2022; 12(1):105. https://doi.org/10.3390/min12010105

Chicago/Turabian Style

Shcherbakov, Vasily, Ilya Bindeman, and Viktor Gazeev. 2022. "Geochemical, Isotopic and Petrological Constraints on the Origin and Evolution of the Recent Silicic Magmatism of the Greater Caucasus" Minerals 12, no. 1: 105. https://doi.org/10.3390/min12010105

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