Geochronology of eruptions and parental magma sources of Elbrus volcano,the Greater Caucasus: K-Ar and Sr-Nd-Pb isotope data |
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| Authors: | V A Lebedev I V Chernyshev A V Chugaev Yu V Gol’tsman E D Bairova |
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| Institution: | 1.Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry,Russian Academy of Sciences,Moscow,Russia |
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| Abstract: | Complex geochronological and isotope-geochemical studies showed that the Late Quaternary Elbrus volcano (Greater Caucasus)
experienced long (approximately 200 ka) discrete evolution, with protracted periods of igneous quiescence (approximately 50
ka) between large-scale eruptions. The volcanic activity of Elbrus is subdivided into three phases: MiddleNeopleistocene (225–170
ka), Late Neopleistocene (110–70 ka), and Late Neopleistocene-Holocene (less than 35 ka).
Petrogeochemical and isotope (Sr-Nd-Pb) signatures of Elbrus lavas point to their mantle-crustal origin. It was shown that
hybrid parental magmas of the volcano were formed due to mixing and/or contamination of deep-seated mantle melts by Paleozoic
upper crustal material of the Greater Caucasus. Mantle reservoir that participated in the genesis of Elbrus lavas as well
as most other Neogene-Quaternary magmatic rocks of Caucasus was represented by the lower mantle “Caucasus” source. Primary
melts generated by this source in composition corresponded to K-Na subalkali basalts with the following isotopic characteristics:
87Sr/86Sr = 0.7041 ± 0.0001, ƒNd = +4.1 ± 0.2, 147Sm/144Nd = 0.105–0.114, 206Pb/204Pb = 18.72, 207Pb/204Pb = 15.62, and 208Pb/204Pb = 38.78. The temporal evolution of isotope characteristics for lavas of Elbrus volcano is well described by a Sr-Nd mixing
hyperbole between “Caucasus” source and estimated average composition of the Paleozoic upper crust of the Greater Caucasus.
It was shown that, with time, the proportions of mantle material in the parental magmas of Elbrus gently increased: from ∼60%
at the Middle-Neopleistocene phase of activity to ∼80% at the Late Neopleistocene-Holocene phase, which indicates an increase
of the activity of deep-seated source at decreasing input of crustal melts or contamination with time. Unraveled evolution
of the volcano with discrete eruption events, lacking signs of cessation of the Late Neopleistocene-Holocene phase, increasing
contribution of deep-seated mantle source in the genesis of Elbrus lavas with time as deduced from isotope-geochemical data,
as well as numerous geophysical and geological evidence indicate that Elbrus is a potentially active volcano and its eruptions
may be resumed. Possible scenarios were proposed for evolution of the volcano, if its eruptive activity were to continue. |
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