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- MakaleAçık Erişim2022Scopus SJRQ240Ar–39 Ar dating, whole-rock and Sr-Nd isotope geochemistry of the Middle Eocene calc-alkaline volcanic rocks in the Bayburt area, Eastern Pontides (NE Turkey): Implications for magma evolution in an extension-related setting
Kaygusuz, Abdullah; Yücel, Cem; Aydınçakır, Emre; Gücer, Mehmet Ali; Ruffet, Gilles
Discussions continue about whether Middle Eocene magmatism in the Eastern Pontides is associated with collision or subduction. This paper presents new whole-rock geochemistry, Sr-Nd isotopic and 40Ar-39Ar age data for Middle Eocene volcanic rocks from the Bayburt area of the Eastern Pontides (NE Turkey) to investigate their sources and evolutionary history. The new 40Ar–39Ar ages reveal that these volcanic rocks erupted between 44.6 ± 0.1 Ma and 43.5 ± 0.1 Ma, within the Lutetian (Middle Eocene). The studied volcanic rocks are composed of basalt, andesite, basaltic andesite and minor dacite lava and pyroclastic rocks. These rocks consist of plagioclase, amphibole, pyroxene, olivine, biotite, sanidine and minor quartz phenocrysts with Fe-Ti oxides. They have microlithic, hyalo-microlithic, porphyritic and rarely glomeroporphyritic textures. The volcanic rocks have low to high-K calc-alkaline affinities. They display enrichment in large-ion lithophile elements and depletion in high-field strength elements with high Th/Yb ratios, which indicate that the magmas forming the volcanic rocks were derived from lithospheric mantle sources enriched by mostly slab-derived fluids in the spinel stability field. 87Sr/86Sr(i) values vary between 0.70485 and 0.70551 and 143Nd/144Nd(i) values vary between 0.51255 and 0.51267. These data correspond to the mantle array on the isotope ratio diagram. The main solidification processes consist of fractional crystallization with minor assimilation. In light of the data obtained in this study together with data from previous studies, petrogenetic character of the Middle Eocene magmas from the southern parts of the Eastern Pontides may be explained by melting of an enriched lithospheric mantle source initially metasomatized by subduction fluids in a post-collisional extensional-related tectonic setting.
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İncele - MakaleYalnız künye2009Scopus SJRQ3K/Ar ages and geochemistry of the post-collisional volcanic rocks in the Mica (Erzurum) area, eastern Turkey
Kaygusuz, Abdullah
The Neogene Ilica volcanics in eastern Anatolia are of sub-alkaline affinity and present features of post-collisional volcanism. The lava flows in the Ilica area reveal K/Ar ages ranging from 13.9 ± 0.5 to 4.4 ± 0.3 Ma, corresponding to the Miocene- and Pliocene age. The volcanic rocks are composed of calc-alkaline basaltic trachyandesitic-, trachyandesitic-, andesitic- and minor dacitic lavas associated with pyroclastics, with the andesitic lavas being volumetrically the most abundant. Some special textures, such as the dissolution/melting and poikilitic type, and the normal, reverse, and oscillatory zoning in the plagioclase- and pyroxene phenocrysts are attributable to disequilibrium crystallization related to magma mixing. The rocks are characterized by enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE), with pronounced depletion of high field strength elements (HFSE). They show depletion in Nb and Ta, indicating the role of crustal contamination. The rocks also have moderately fractionated rare earth elements (REE) patterns with (La/Lu)N ratios of 10-19 for andesitic- and dacitic rocks, and 7-10 for basaltic trachyandesitic- and trachyandesitic rocks. Basaltic trachyandesites show slightly positive Eu anomalies, whereas the deepening of Eu through gradual increase from trachyandesite to dacite, indicating a genetic link between the basaltic trachyandesite and the dacites. The main solidification processes consist of magma mixing and fractional crystallization with minor amounts of crustal contamination which were operative during the solidification of the volcanic rocks. All evidences support the theory that Ilica volcanic rocks were derived from partial melting of lower continental crust, having undergone interaction with subcontinental lithospheric mantle in a post-collisional geodynamic setting.
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