Alkaline magmas in zones of continental convergence: The Tezhsar volcano-intrusive ring complex, Armenia

Autor: Gevorg Navasardyan, Krzysztof Sokół, Khachatur Meliksetian, Ralf Halama, Ivan P. Savov, Masafumi Sudo
Rok vydání: 2018
Předmět:
Zdroj: Lithos. :172-191
ISSN: 0024-4937
DOI: 10.1016/j.lithos.2018.08.028
Popis: Alkaline igneous rocks are relatively rare in settings of tectonic convergence and little is known about their petrogenesis in these settings. This study aims to contribute to a better understanding of the formation of alkaline igneous rocks by an investigation of the Tezhsar volcano-intrusive alkaline ring complex (TAC) in the Armenian Lesser Caucasus, which is located between the converging Eurasian and Arabian plates. We present new petrological, geochemical and Sr-Nd isotope data for the TAC to constrain magma genesis and magma source characteristics. Moreover, we provide a new 40Ar/39Ar age of 41.0±0.5 Ma on amphibole from a nepheline syenite that is integrated into the regional context of ongoing regional convergence and widespread magmatism. The TAC is spatially concentric and measures ~10 km in diameter representing the relatively shallow plumbing system of a major stratovolcano juxtaposed by ring faulting with its extrusive products. The plutonic units comprise syenites and nepheline syenites, whereas the extrusive units are dominated by trachytic-phonolitic rocks. The characteristic feature of the TAC is the development of pseudomorphs after leucite in all types of the volcanic, subvolcanic and intrusive alkaline rocks.\ud 40 Whole-rock major element data show a metaluminous (Alkalinity Index = 0-0.1), alkalic and silica-undersaturated (Feldspathoid Silica-Saturation Index
Databáze: OpenAIRE
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