Browsing by Author "Oyan, V."

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Geochemical Evaluation of the Late Maastrichtian Subduction-Related Volcanism in the Southern Neotethys in Van Area, and a Correlation Across the Turkish-Iranian Border
(Universita degli Studi di Firenze, 2014) Çolakoğlu, A.R.; Günay, K.; Göncüoğlu, M.C.; Oyan, V.; Erdoğan, K.
The Yüksekova mélange to the NE of Van, close to the Turkish-Iranian border is part of the Berit-Elazığ-Van ophiolitic belt. It structurally overlies the Bitlis-Pütürge metamorphic complex and includes the remnants of the southern Neotethys. The mélange complex comprises mantle rocks together with massive and pillowed lavas and dykes associated with late Maastrichtian micritic limestones and radiolarian cherts. The lavas are trachyandesite/basaltic, whereas the dykes are alkali basalt in composition. Both rock types were probably formed by low-degree partial melting of a mixed source including primitive mantle and depleted MOR mantle components, which were subsequently affected by subduction modification. The geochemical character constrains the formation of these basalts, yet the youngest ones dated in the Yüksekova mélange to an intra-oceanic subduction zone within the Neotethys at the end of Cretaceous. The new ages and the tectonic setting of the volcanic rocks are correlated with other oceanic assemblages (e.g., Khoy and Inner Zagros ophiolites in Iran) across the Turkish-Iranian border. © 2014, Universita degli Studi di Firenze. All Rights Reserved.
The Geochronology and Origin of Mantle Sources for Late Cenozoic Intraplate Volcanism in the Frontal Part of the Arabian Plate in the Karacadag Neovolcanic Area of Turkey. Part 1. The Results of Isotope-Geochronological Studies
(Pleiades Publishing inc, 2012) Keskin, M.; Chugaev, A. V.; Lebedev, V. A.; Sharkov, E. V.; Oyan, V.; Kavak, O.
This paper considers results from isotope-geochronological (K-Ar) studies of the products of Neogene-Quaternary volcanism in the Karacadag area, which is situated within the northern frontal part of the Arabian plate. It was found that magmatic activity has been evolving at this location for at least the last 11-10 Myr and was distinctly discrete in character. Three stages of volcanism have been identified: (I) Early or Miocene, similar to 11-6.7 Ma; (II) Middle or Pliocene-Early Quaternary, 4-1 Ma; and (III) Late or Late Quaternary, 0.4-0.1 Ma. The most recent manifestations of magmatic activity in the region date back to about 100000 years ago. An analysis of the spatial distribution of volcanic centers of different ages in the Karacadag neovolcanic area shows that the magmatism of that region involved a lateral migration of activity from northwest to southeast along a major regional tectonic fault. The migration was caused by the movement of local tension zones where the lithosphere was thinner and deep-seated mantle magmas were ascending.
The Geochronology and Origin of Mantle Sources for Late Cenozoic Intraplate Volcanism in the Frontal Part of the Arabian Plate in the Karacadag Neovolcanic Area of Turkey. Part 2. The Results of Geochemical and Isotope (sr-Nd Studies
(Pleiades Publishing inc, 2012) Keskin, M.; Chugaev, A. V.; Lebedev, V. A.; Sharkov, E. V.; Oyan, V.; Kavak, O.
A geochemical and isotope-geochemical (Sr-Nd-Pb) study has been carried out for the Karacadag neovolcanic area, which is situated within the frontal part of the Arabian plate. The obtained data and the results of petrological modeling show that the petrogenesis of parental magmas in the Karacadag neovolcanic area involved two compositionally different mantle sources; one consisted of garnet-bearing peridotites of the asthenosphere mantle and the other was spinel-bearing peridotites of the enriched subcontinental lithosphere mantle. During early stages in the evolution of the magmatic system, deep-seated asthenospheric magmas were ascending to the surface while intensively interacting with the melts that had been generated at upper mantle depths. The interaction gradually diminished, so that the later effusive rocks mostly have compositions that are similar to those of the primitive asthenospheric magmas. It is shown that a significant (up to 17-18 wt % of the mantle melt) assimilation of crustal material could take place only during the initial phases of the magmatism. Periodic replenishment of the magma chambers by primitive magmas, which resulted in an observable high degree of homogeneity in the composition of young effusive rocks, was also of importance in the petrogenesis of lavas during the evolution of volcanic activity.
Geochronology of Late Cenozoic Volcanism in the Area of Lake Van, Turkey: an Example of Developmental Dynamics for Magmatic Processes (Vol 433, Pg 1031, 2010)
(Maik Nauka/interperiodica/springer, 2010) Lebedev, V. A.; Sharkov, E. V.; Keskin, M.; Oyan, V.
An isotope-geochronological study has been performed to examine the products of Late Cenozoic collision volcanism on the northern coast of Lake Van, Turkey. We obtained 45 new K-Ar dates, based on which the principal time characteristics of volcanic activity in the region have been determined. Volcanic activity in the northern coast of Lake Van has lasted similar to 15 myr; it has had an expressed discrete nature, when periods of intense volcanic activity alternated with long-lasting pose periods. Four stages of Neogene-Quaternary volcanism have been identified: Middle Miocene (15.0-13.5 Ma), Late Miocene (10-9 Ma), Pliocene (5.8-3.7 Ma), and Quaternary (1.0-0.4 Ma). The average duration of the stages was 1-2 myr; the stages were separated from each other with periods of inactivity of approximately equal lengths (similar to 3 myr). For each of the Pliocene and Quaternary stages, three additional phases of volcanism have been identified, which were separated from each other with short time intervals (a few hundred thousand years). The last burst of volcanic activity in the study area occurred similar to 400 ka; similar to Quaternary volcanism in general, it was not characterized by a high intensity. An important result of the studies performed was to confirm the existence of a separate Middle Miocene stage of collision volcanism for the Caucasian-Anatolian Segment of the Alpine Fold Belt. New geochronological data generated presented in this paper indicate that Neogene-Quaternary volcanism in this portion of the belt started much earlier (similar to 15 Ma) than assumed by the majority of the previous researchers.
Geochronology of Late Cenozoic Volcanism in the Area of Van Lake, Turkey: an Example of Development Dynamics for Magmatic Processes
(2010) Lebedev, V.A.; Sharkov, E.V.; Keskin, M.; Oyan, V.
An isotope-geochronological study has been performed to examine the products of Late Cenozoic collision volcanism on the northern coast of Van Lake, Turkey. We obtained 45 new K-Ar dates, based on which the principal time characteristics of volcanic activity in the region have been determined. The total duration of magmatic activity in the area of the northern coast of Van Lake has lasted 15 myr; it has had an expressed discrete nature, when periods of intense volcanic activity alternated with lasting breaks in eruptions. Four stages of Neogene-Quaternary volcanism have been identified: Middle Miocene (15.0-13.5 myr), Late Miocene (10-9 myr), Pliocene (5.8-3.7 myr), and Quaternary (1.0-0.4 Ma). The average duration of the stages has been 1-2 myr; the stages were separated from each other with periods of inactivity of approximately equal lengths (3 myr). For each of the Pliocene and Quaternary stages, three additional phases of volcanism have been identified, which were separated from each other with short time intervals (a few hundred thousand years). The last burst of volcanic activity in the area in question took place 400 ka; similar to Quaternary volcanism in general, it was not characterized by a high intensity. An important result of the studies performed was to confirm the existence of a separate Middle Miocene stage of collision volcanism for the Caucasian-Anatolian Segment of the Alpine Fold Belt. The data generated allow concluding that Neogene-Quaternary volcanism in this portion of the belt started much earlier (15 Ma) than assumed by the majority of the previous researchers. © 2010 Pleiades Publishing, Ltd.
The Role of Capillary Water Absorption Characteristics of Ignimbrites on the Deterioration of Ahlat Seljuk Tombstones
(TMMOB - Jeoloji Muhendisleri Odasi, 2016) Akin, M.; Dinçer, İ.; Özvan, A.; Oyan, V.; Tapan, M.
The Seljuk Tombs of the Seljuk Empire in the Ahlat region are included in UNESCO’s World Heritage Tentative List due to the fact that the tombstones are known to be the largest graveyards of Muslims with their historical significance. Tombstones were erected using ignimbrite type pyroclastic rocks which are widespread in the region, and several inscriptions and patterns were carved on them thanks to their softness and easy processing. However, these tombstones have been subjected to weathering effects for almost a duration of 800 years. The most striking point after the inspection of tombstones is that many of them were broken from the middle section. In this study, experimental studies were carried out on fresh ignimbrite specimens and particularly the effect of capillary water absorption on deterioration was investigated to reveal the factors leading to deterioration of Ahlat Seljuk tombstones. Accordingly, high porosity and capillary water absorption characteristics of the ignimbrites are found to be the major reasons for the deterioration of tombstones. © 2016, TMMOB - Jeoloji Muhendisleri Odasi. All rights reserved.
Sources and Evolution of Miocene-Pleistocene Alkaline Magmatism in the Northeast Part of the Arabian Plate: Evidence From Sr-Nd Isotope Data and K-Ar Geochronometry
(Maik Nauka/interperiodica/springer, 2024) Chugaev, A. V.; Parfenov, A. V.; Lebedev, V. A.; Chernyshev, I. V.; Oyan, V.; Ozdemir, Y.; Pavlidis, S. B.
A geochronological and isotope-geochemical study of alkaline basalts from three areas of young magmatism within the northeastern part of the Arabian Plate (Southeastern Turkey), Batman, Kurtalan and Alemdag, was carried out. The obtained isotope data have indicated that the volcanism in the studied region developed over a 5-Ma period from the end of Miocene to the middle Pleistocene during four pulses separated by breaks in magmatic activity: 6.1-4.9 Ma (Batman area, hawaiites), similar to 3.0 Ma (Alemdag plateau, phase I, basalts), 2.0-1.9 Ma (Alemdag plateau, phase II, tephrites), and 1.5-1.3 Ma (Alemdag plateau, phase III, basalts; Kurtalan area, basalts). A comparison of spatial-temporal changes of magmatic activity evolution in the studied part of the Arabian Plate and within the largest basalt plateau of Arabian foreland, Karacadag Plateau, located to the west, was carried out. The results of Sr-Nd-Pb isotope-geochemical studies show that the development of young basalt volcanism in the Arabian Plate was characterized at different time by the contribution of various mantle sources in magma generation under this region. Initial pulses of magmatic activity are associated with melting of Arabian subcontinental lithospheric mantle (SCLM). The processes of fractional crystallization combined with crustal assimilation (AFC) have played an important role in the petrogenesis of lavas as well. Later, a deep mantle source (PREMA) with a depleted isotopic composition played a leading role in the formation of basaltic magmas of increased alkalinity. The melts generated by this source were mixed with the SCLM material in various proportions at different stages of magmatism with a limited participation of AFC processes in the petrogenesis of the rocks. It was concluded that young basalt volcanism of increased alkalinity in the northeast of the Arabian Plate is not related to the collision of the Eurasian and Arabian plates genetically, but presumably manifested here as a result of the migration of the initial rift geodynamic setting from the Red Sea basin to the north along Levantine and East Anatolian transform faults due to directed convection flows in the lower part of mantle under this part of the Earth.