Vural Oyan

Geochronology of Late Cenozoic Volcanism in the Area of Van Lake, Turkey: An Example of Development Dynamics for Magmatic Processes

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.

The geochronology and origin of mantle sources for late cenozoic intraplate volcanism in the frontal part of the Arabian plate in the Karacadağ neovolcanic area of Turkey. Part 2. The results of geochemical and isotope (Sr-Nd-Pb) studies

A geochemical and isotope-geochemical (Sr-Nd-Pb) study has been carried out for the Karacadağ 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 Karacadağ 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.

The geochronology and origin of mantle sources for late cenozoic intraplate volcanism in the frontal part of the Arabian plate in the Karacadağ neovolcanic area of Turkey. Part 1. The results of isotope-geochronological studies

This paper considers results from isotope-geochronological (K-Ar) studies of the products of Neogene-Quaternary volcanism in the Karacadağ 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, ∼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 Karacadağ 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.

Erratum: Geochronology of Late Cenozoic Volcanism in the Area of Lake Van, Turkey: An Example of Developmental Dynamics for Magmatic Processes ( Doklady Earth Sciences, 433(2), pp. 1031-1037)

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 ∼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 (∼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 ∼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 (∼15 Ma) than assumed by the majority of the previous researchers.

Petrology and Geochemistry of the Quaternary Mafic Volcanism to the NE of Lake Van, Eastern Anatolian Collision Zone, Turkey

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/Sr and Pb isotopic ratios and lower Nd/Nd 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 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.