Browsing by Author "Chugaev, Andrey V."

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Au-Rich Bimodal-Mafic Type Volcanogenic Massive Sulphide Deposit Associated With Jurassic Arc Volcanism From the Central Pontide (Kastamonu, Turkey)
(Elsevier, 2022) Gunay, Kurtulus; Oyan, Vural; Donmez, Cahit; Cavdar, Bugra; Ciftci, Emin; Chugaev, Andrey V.; Ma, Chang-Qian
The central part of the Pontide Orogenic Belt, located in northern Anatolia, is a segment of the Alpine-Himalayan orogeny. Cangaldag Metamorphic Complex (CMC) occurs within this segment which consists of ensimatic island arc volcanics and deep sea sediments which occasionally cut cross by mafic sills/dykes. They were exposed to metamorphism under the greenschist facies conditions and remain in tectonic contact with each other. The Say yayla mineralization is one of the recently discovered volcanogenic massive sulfide (VMS) deposits in the CMC with a remarkable Au content. The mafic and felsic metavolcanic rocks are the host-rocks of the Say Yayla mineralization and the ages determined by U-Pb zircon grains of these felsic volcanic rocks range from 170 Ma to 165 Ma indicating Middle Jurassic time. At the 0.1% cut-off grade, 7.5 million tons of resource has been calculated with 0.75 ppm Au, 0.65 wt% Cu, and 0.35 wt% Zn grades. The Say Yayla mineralization consists of massive and semi-massive sulfide minerals and a mineral assemblage represented by predominantly pyrite and chalcopyrite and trace amounts of sphalerite, tennantite and galena. Average base and precious metal grades of the zones occur with >1 wt% Cu are 2 wt% for Cu, 0.7 wt% for Zn, 0.04 wt% for Pb and 1.5 g/t for Au. The sulfur isotope values (delta S-34 VCDT) range from 4.9 parts per thousand to 6.7 parts per thousand for pyrite grains and 4.2 parts per thousand was obtained from the one sphalerite sample. delta O-18 values for the quartz from quartz-rich ore samples were 10.6 parts per thousand and 11.7 parts per thousand delta O-18 (VSMOW)(qtz). delta O-18 (VSMOW)(fluid) values for the ore-forming fluids vary between 0 parts per thousand and 2.4 parts per thousand. Lead isotope compositions of the pyrite minerals were 18.148-18.150 (Pb-206/Pb-204), 15.548-15.550 (Pb-207/Pb-204) and 38.078-38.083 (Pb-208/Pb-204) The geological, geochemical, and isotopic data of the ore and host-rocks reveal that the mineralization is a bimodal-mafic type (Noranda type), which is classified into Cu-Zn group of volcanogenic massive sulfides. Geochemical and geochronological data from the wall rocks further show that mineralization was developed within an ensimatic island arc environment during the Middle Jurassic.
Magmatic Evolution of the Early Pliocene Etrusk Stratovolcano, Eastern Anatolian Collision Zone, Turkey
(Elsevier, 2016) Oyan, Vural; Keskin, Mehmet; Lebedev, Vladimir A.; Chugaev, Andrey V.; Sharkov, Evgenii V.
The Pliocene Etrusk stratovolcano, located in the northeast of Lake Van (Eastern Anatolia; Turkey), is one of the important volcanic centres in the Eastern Anatolian collision zone. Mt. Etrusk overlies a widespread volcanic plateau, consisting of basaltic and hawaiitic lavas formed by fissure eruptions between 4.9-4.5 Ma. These basic lavas contain a phenocryst phase consisting of olivine, plagioclase and clinopyroxene. Trace element ratio diagrams imply that these basic magmas were generated from a mantle that contained a clear subduction component that is related to the subducted sediments rather than fluids or altered oceanic crust. Results of the melting models on the basaltic plateau lavas indicate that there was a marked variation both in the mantle source mineralogy (i.e. the ratio of garnet peridotite to spinel peridotite in the source varies between 60/40% and 40/60%) and the degree of melting (i.e. F between 0.8-4%). This can be explained by a model in which magmas were generated by partial melting of both metasomatised lithospheric and deeper asthenospheric mantle sources in an extensional setting in response to the partial delamination of the lithospheric mantle of Eastern Anatolia and then mixed with each other during Pliocene times. Central eruptions that formed the Etrusk volcano lasted similar to 600 kyr between 43-3.7 Ma during Zanclean times. The estimated depth of the Etrusk magma chamber is similar to 9-12 km. The volcano erupted lavas with a rather narrow compositional range from latite to rhyolite, which are either transitional or mildly alkaline in character. The Etrusk lavas contain plagioclase, clino- and orthopyroxene, biotite, K-feldspar and rarely, minor amounts of olivine and amphibole in the phenocryst phase. A composite chemo-stratigraphic section of the volcano and petrological models indicate that the evolved lavas of the Etrusk volcano differentiated from a parental magma composition, which is similar to that of the most primitive plateau basalt lavas underlying the volcano, via the AFC process, and experienced at least two major magma replenishment episodes at 4.1 Ma and 3.8 Ma during the magma chamber evolution. (C) 2016 Elsevier B.V. All rights reserved.
Petrogenesis of Miocene To Quaternary Primitive Basaltic Magmas in the Area of Lake Van (East Anatolia, Turkey): a Case for Relamination of Mantle Lithosphere After Lithospheric Delamination
(Springer, 2023) Oyan, Vural; Ozdemir, Yavuz; Chugaev, Andrey V.; Oyan, Elif; Chernyshev, Igor V.
We present the geochemical and Sr-Nd-Pb isotopic data and the petrological evolution of primitive basaltic lavas that erupted from the Miocene to Quaternary in the East Anatolia Collision Zone to understand the geodynamic conditions and the change in the lithospheric mantle over time. Major trace element abundances, Sr-Nd-Pb isotopic compositions and petrological models show that the primitive basaltic samples were not affected by crustal contamination and fractional crystallization. They are derived from a depleted MORB mantle modified by melts derived from subducted sediments. The primitive melts of the Miocene and Quaternary series were derived from an amphibole-bearing garnet lherzolitic mantle and an amphibole-bearing garnet-spinel lherzolite mantle source, respectively. In contrast, the Pliocene basaltic melts were formed by mixing melts originating from both an amphibole-bearing spinel and garnet lherzolite. Our thermodynamic calculations indicate that the lithosphere-asthenosphere boundary (LAB) is about 30 km shallower in the Pliocene than in the Miocene.This may be explained by lithospheric delamination in the Early Pliocene. In contrast, the LAB in the Quaternary is approximately 9 km deeper than in the Pliocene, which can be explained by relamination of the mantle lithosphere. Thermal calculations have shown that about 5-11 km of the relamination can occur within 5-6 Ma and that asthenospheric melts can relaminate the base of the thinned lithospheric mantle by cooling, and the presence of the relaminated mantle lithosphere is documented throughout the whole EACZ.
Petrology and Geochemistry of the Quaternary Mafic Volcanism To the Ne of Lake Van, Eastern Anatolian Collision Zone, Turkey
(Oxford Univ Press, 2017) Oyan, Vural; Keskin, Mehmet; Lebedev, Vladimir A.; Chugaev, Andrey V.; Sharkov, Evgenii V.; Unal, Esin
Collision-related Quaternary mafic volcanism to the north of Lake Van (Eastern Anatolia, Turkey) occurred by eruptions from both volcanic centres and extensional fissures trending approximately north-south. We report new major, trace and rare earth element abundances, Sr-Nd-Pb isotope ratios and K-Ar ages for basaltic and more evolved hawaiitic and mugearitic lava flows. The new K-Ar ages indicate that magmatic activity occurred between 1.0 and 0.4 Ma. The volcanic products consist of mildly alkaline lavas, ranging in composition from basalt to hawaiite and mugearite. Energy-constrained assimilation and fractional crystallization (EC-AFC) model calculations suggest that the least evolved basaltic samples were unaffected by the combined effects of fractional crystallization and crustal contamination processes, in contrast to the more evolved hawaiitic and mugearitic lavas, which have experienced up to 2-3% crustal assimilation. Calculations based on crustal temperatures and Curie point depths indicate that the magma chamber, from which the basic to evolved lavas were derived, might be located at a depth of around 6-8 km, within the upper crust. Enrichment of large ion lithophile elements and light rare earth elements relative to high strength field elements, and higher Sr-87/Sr-86 and Pb isotopic ratios and lower Nd-144/Nd-143 of the least evolved basaltic samples indicate that the mantle source region of the Quaternary mafic magmas might have been enriched by melts that were derived from subducted sediments with a partial melting degree of around 10% rather than from Altered Oceanic Crust melts and fluids. Our model melting calculations show that the basaltic melts might have been produced by melting of a mantle source containing both amphibole and garnet with a partial melting degree of similar to 3%. Results of our petrological models indicate that a metasomatized mantle source, which was infiltrated by a mixture of 93% mantle melt and 7% sediment melt plus 0.01% residual rutile, added to mantle melt, could have been the source composition of the basaltic melts that produced the Quaternary mafic volcanism.