Browsing by Author "Ozdemir, Yavuz"

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Composition, Pressure, and Temperature of the Mantle Source Region of Quaternary Nepheline-Basanitic Lavas in Bitlis Massif, Eastern Anatolia, Turkey: a Consequence of Melts From Arabian Lithospheric Mantle
(Elsevier Science Bv, 2019) Ozdemir, Yavuz; Mercan, Cagri; Oyan, Vural; Ozdemir, Ayse Atakul
The Quaternary (0.66-0.63 Ma) nepheline basanites (ne - basanite) are the firstly observed volcanic products of Arabia-Eurasia collision on Bitlis Pottirge Massif. They composed of clinopyroxene, olivine, Ti-magnetite, Cr spinel, and nepheline. The forsterite compositions of olivines range between 73 and 83%, calcic clinopyroxenes show modest variations in Wo(48-57)-En(37-45)-FS5-7 and nephelines occur as minor minerals within the networks of other groundmass minerals. They are characterized by low SiO2 (40.16-41.96 wt%), high MgO contents (8.54-9.73 wt%) and similar Sr-Nd isotopic compositions with Arabian Plate volcanics. Mineral and whole rock thermobarometry yield crystallization pressure and a temperature range between 8 and 20 kbar and 1301 degrees C - 1035 degrees C respectively. Lavas have high Mg -number (>0.58), high Cr and Ni contents and strong LREE enrichment but depletion in Rb, K, and Pb. Trace elements together with Sr isotopic compositions inferred negligible assimilation of the local upper crustal material. The calculated average pressure and temperature of mantle melting for ne-basanites is 2,85 kbar and 1353 degrees C respectively. FC3MS (wt% FeO/CaO-3*MgO/SiO2) parameter and melting models using REE data reveal catak basanites are products of amphibole and phlogopite bearing metasomatised lithospheric mantle in garnet stability field. They seem to originated from depths of similar to 85 km which corresponds to the base of the Arabian lithosphere in the region. (C) 2019 Elsevier B.V. All rights reserved.
A Debris Avalanche at Suphan Stratovolcano (Turkey) and Implications for Hazard Evaluation
(Springer, 2016) Ozdemir, Yavuz; Akkaya, Ismail; Oyan, Vural; Kelfoun, Karim
The Quaternary Suphan debris avalanche deposit is located in Eastern Anatolia, Turkey. The avalanche formed by the sector collapse of a major stratovolcano towards the north, possibly during a single catastrophic event. The deposit has an estimated volume of 4 km(3) and ran out over 25 km to cover an area of approximately 200 km(2). Products of the collapse are overlain by younger eruptive units from the Suphan volcano. We have tested the numerical code VolcFlow to first reproduce the emplacement of the Quaternary Suphan debris avalanche and then to develop a hazard assessment for potential future sector collapses and subsequent emplacement of debris avalanches and associated tsunami. The numerical model captures the main features of the propagation process, including travel distance, lateral spread, and run up. The best fit obtained for the existing flow has a constant retarding stress of 50 kPa and a collapse scar volume of 4 km(3). Analysis of potential future collapse scenarios reveals that northern sector debris avalanches (up to 6 km(3)) could affect several towns. In the case of a sector collapse towards the south, a tsunami will reach the city of Van and several of the biggest towns on the southern shoreline of Lake Van. Cities most affected by the larger amplitude waves would be Van, Edremit, Gevas, Tatvan, and, to a lesser extent, Ercis, with wave amplitudes (first waves after the onset of the collapse) between 8 and 10 m.
Deciphering the Magma Storage Conditions and Preeruptive Processes at Cuma?ay: a Plio-Quaternary Volcanic Eruption Center in Eastern Anatolia, Turkey
(Tubitak Scientific & Technological Research Council Turkey, 2023) Ozdemir, Yavuz; Ozdemir, Ayhan
We investigate the geology and petrology of Cumacay, one of the Plio-Quaternary eruption centers of postcollisional volcanism in Eastern Turkey, using a combination of geochronology, bulk-rock geochemistry, thermobarometry, and thermodynamic simulations. Our new K-Ar ages reveal an age of 3.5-0.97 Ma for the eruptive products, which spread around an area of approximately 1000 km2. Mineral-melt equilibria for olivine, orthopyroxene, clinopyroxene, and plagioclase allow estimation of crystallization pressures, and temperatures indicate two separate crustal storage of crystallization at 14-28 km and 5-15 km. The temperature estimation from diverse methods ranges from 954 & DEG;C to 1224 & DEG;C. Thermodynamic modelings using Magma Chamber Simulator (MCS) at a representative pressure (5 kbar) imply that the assimilation and crustal contamination (AFC) resulted in evolved melts with various SiO2 contents at mid to lower crustal depths. Calculated wide range of temperatures, compositional variety from evolved members, and MCS recharge simulation at a representative pressure (2.5 kbar) reveal that the magma mixing between contrasted melts characterizes the final chemical dispersal of the erupted lavas.
Discovery and Environmental Implications of Santorini Tephras (Cape Riva and Minoan) in Sediments of Lake Yayla (West Anatolia)
(Sage Publications Ltd, 2025) Dogan, Mustafa; Ozdemir, Yavuz; Bozkurt, Yunus; Senkul, Cetin
Throughout the long eruption history of the Santorini volcano, the Cape Riva/Y-2 and Minoan/Z-2 eruptions had a profound impact on the environment. The Minoan eruptions also had a significant impact on society. These two tephras, as well as the Y-2 tephra individually, have been recorded for the first time in a lacustrine area in western Anatolia. This study examines the geochemical properties of Y-2 (23 cm) and Z-2 tephra layers (19 cm; 14 cm pure and 5 cm mixed) from 18 m sediment cores in Lake Yayla (Denizli-Buldan). Additionally, high-resolution mu XRF, fossil pollen, charcoal, and dating analyses were conducted on the cores to determine the chronologies and environmental effects of the tephra layers. Fossil pollen findings show consistent forest and steppe/grassland vegetation before and after the Z-2 tephra, with the forest impact lasting for 240 years after the eruption. Increased aquatic vegetation and changes in specific taxa (e.g. Pinus sp. and Amaranthaceae increased, while Quercus deciduous, Olea europaea, and cereals decreased) were observed following the Minoan eruption. Charcoal analysis indicates heightened fire activity post-Minoan eruption, while XRF data reveal no associated climatic change. At the same time, no correlation has been identified between the Cape Riva eruption and ecological changes (climate, vegetation, and fire activity). Contribution to dating the tephra was provided by radiocarbon dating from the lowest part of the tephra layer (17,684 +/- 63 years BP). This study sheds light on the extensive impacts of the Y-2 and Z-2 tephra eruptions, focusing on their dating, geochemistry, environmental effects, tephra transport directions, and thicknesses. It demonstrates the presence of a significant geological event for the settlements in the B & uuml;y & uuml;k Menderes Valley.
Discovery and Environmental Implications of Santorini Tephras (Cape Riva and Minoan) in Sediments of Lake Yayla (West Anatolia) (Sept, 10.1177/09596836241275007, 2024)
(Sage Publications Ltd, 2025) Dogan, Mustafa; Ozdemir, Yavuz; Bozkurt, Yunus; Gurboga, Sule; Senkul, Cetin
The Geo/Thermochronology of Dismal Island (Marguerite Bay, Antarctic Peninsula)
(Tubitak Scientific & Technological Research Council Turkey, 2023) Karaoglan, Fatih; Karatas, Burcu; Ozdemir, Yavuz; Gulyuz, Erhan; Vassilev, Oleg; Selbesoglu, Mahmut Oguz; Gildir, Semih
Dismal Island is located at the entrance of Marguerite Bay between Adelaide Island to the northeast and Alexander Island to the southwest within the Antarctic Peninsula (AP). Its unique position between Alexander and Adelaide islands provides the opportunity to perform testing and link these regions through Cenozoic magmatism and tectonics due to the subduction of the Pacific plate beneath the AP along the northern margin. Dismal Island was visited in February 2021 within the framework of the sixth Turkish Antarctic Expedition (TAE-VI). Thirteen samples were collected for petrography, geochronology, and low-temperature thermochronology (LTT). Of the samples, 3 were dated using laser ablation-inductively coupled plasma-mass spectrometer zircon U-Pb geochronology, 2 were dated using apatite fission-track (AFT) analysis, and 1 was dated using apatite uranium-thorium-helium (U-Th/He) (AHe) thermochronology. The island comprises massif quartz-diorite, tonalite, mafic, and felsic dikes, indicating a hybrid magma source. The 3 zircon U-Pb ages yielded a crystallization age of 47-48 for the magmatic body. The AFT ages yielded a cooling age of 41 Ma, suggesting either a shallow emplacement at a depth of similar to 4 km or an uplift/exhumation during middle-late Eocene boundary. In contrast, the AHe age of 1 sample was 20.1 +/- 1.1 Ma, together with a fast-cooling profile during the same period, which indicated an early Miocene uplift in the region. Similar early-middle Eocene crystallization ages within similar rock outcrops were determined on Adelaide and Alexander islands, Adelaide Island Intrusive Suite. The AFT ages obtained in this study (similar to 41 Ma), close to formation age, were also found on Adelaide and Alexander islands. The (LTT) literature of the region shows that the LTT ages get younger to the north along the AP, reflecting the northward migration of the ridge-trench collision and opening of the slab window along the western coast of the AP. The AHe age and the fast-cooling profile suggested that the ridge-subduction between the Tula and Adelaide fracture zones to the north of Dismal Island reached the region during Aquitanian-Burdigalian.
Geochemistry and Origin of Plagiogranites From the Eldivan Ophiolite, Cankiri (Central Anatolia, Turkey)
(Slovak Acad Sciences Geological inst, 2014) Uner, Tijen; Cakir, Uner; Ozdemir, Yavuz; Arat, Irem
The Eldivan Ophiolite, exposed around Ankara and Cankiri cities, is located at the central part of the Izmir-Ankara-Erzincan Suture Zone (IAESZ). It represents fragments of the Neotethyan Oceanic Lithosphere emplaced towards the south over the Gondwanian continent during the Albian time. It forms nearly complete series by including tectonites (harzburgites and rare dunites), cumulates (dunites, wherlites, pyroxenites, gabbro and plagiogranites) and sheeted dykes from bottom to top. Imbricated slices of volcanic-sedimentary series and discontinuous tectonic slices of ophiolitic metamorphic rocks are located at the base of tectonites. Plagiogranitic rocks of the Eldivan Ophiolite are mainly exposed at upper levels of cumulates. They are in the form of conformable layers within layered diorites and also dikes with variable thicknesses. Plagiogranites have granular texture and are mainly composed of quartz and plagioclases. The occurrences of chlorite and epidote revealed that these rocks underwent a low grade metamorphism. Eldivan plagiogranites have high SiO2 content (70-75 %) and low K2O content (0.5-1 %) and display flat patterns of REE with variable negative Eu anomalies. LREE/HREE ratio of these rocks varies between 0.2-0.99. All members of the Eldivan rocks have high LILE/HFSE ratios with depletion of Nb, Ti and P similar to subduction related tectonic settings. Geochemical modelling indicates that the Eldivan plagiogranites could have been generated by 50-90 % fractional crystallization and/or 5-25 % partial melting of a hydrous basaltic magma.
Geochemistry of Tholeiitic To Alkaline Lavas From the East of Lake Van (Turkey): Implications for a Late Cretaceous Mature Supra-Subduction Zone Environment
(Pergamon-elsevier Science Ltd, 2016) Ozdemir, Yavuz
Arc-related rocks of the Yuksekova Complex extend from Kahramanmara to Hakkari throughout the Southeast Anatolia representing the remnants of the Southern Branch of Neotethys. The volcanic members of this zone from the eastern parts of Lake Van suggest three different types of rock chemistry; tholeiitic (type I), calc-alkaline (type II) and alkaline (type III). Tholeiitic and calc-alkaline members suggest a subduction-related environment with their HFS and LIL element distributions. RE and trace element systematics and modelings indicate that i) the intermediate and the felsic calc-alkaline rocks are the result of fractional crystallization from a basic endmember, ii) alkaline members have originated from enriched mantle source relative to the tholeiitic and calc-alkaline lavas. Overall data from Yuksekova Complex suggest a mature supra-subduction zone environment within the southern Neotethyan Ocean during Upper Cretaceous time. The existence of Lutetian OIB like asthenospheric lavas at the upper parts of the ophiolitic assemblage in the eastern parts of Lake Van proposes the end of the normal ophiolite formation and the possible continuation of the magmatism with OIB like lavas during Middle Eocene. (C) 2016 Elsevier Ltd. All rights reserved.
Geological and Geochemical Evolution of the Quaternary Suphan Stratovolcano, Eastern Anatolia, Turkey: Evidence for the Lithosphere-Asthenosphere Interaction in Post-Collisional Volcanism
(Oxford Univ Press, 2014) Ozdemir, Yavuz; Gulec, Nilgun
The Suphan stratovolcano is one of the major Quaternary eruption centers of post-collisional volcanism in eastern Anatolia, located in the zone of convergence between the Arabian and the Anatolian plates. We document the geological and geochemical evolution of Suphan in terms of volcanostratigraphy, geochronology (40Ar-39Ar), isotope composition (Sr, Nd, Pb) and bulk-rock geochemistry. Our new 40Ar-39Ar data, along with previously published K/Ar ages, indicate an age of 0 center dot 76-0 center dot 06 Ma for the eruptive products, which extend over an area of similar to 2000 km(2). The products of Suphan include transitional mildly alkaline to calc-alkaline lavas, domes and pyroclastic rocks ranging in composition from basalt to rhyolite. MELTS modeling suggests that the majority of the Suphan magmas with SiO2 contents between similar to 57 and similar to 65 wt % are the products of isobaric-isenthalpic mixing of basaltic trachyandesitic and rhyolitic magmas at a crustal pressure of 0 center dot 5 kbar. Energy-constrained assimilation and fractional crystallization modeling of trace element and isotope compositions points to 2-10% (upper) crustal contamination that accompanied differentiation. Large ion lithophile element enrichment and the presence of negative high field strength element anomalies in primitive mantle-normalized trace element patterns suggest a mantle source that was modified by subducted sediments. Light to heavy and medium to heavy rare earth element ratios and partial melting models suggest the derivation of the eastern Anatolian parental magmas from variable mixing of lithospheric and asthenospheric melts. Unlike the commonly accepted models for post-collisional volcanism that envisage an increasing contribution from asthenospheric melts with time, melting degree and contribution of the lithospheric mantle seem to have increased from Miocene-Pliocene to Quaternary times in eastern Anatolia.
Glass Geochemistry and Tephrostratigraphy of Key Tephra Layers in and Around Lake Van, Eastern Anatolian Volcanic Province (Eavp)
(Pergamon-elsevier Science Ltd, 2025) Kearney, Rebecca J.; Goff, Jeremy; Smith, Victoria; Ozdemir, Yavuz; Schwab, Markus J.; Karaoglu, Ozgur; Brauer, Achim
The volcanoes of Nemrut and Suphan in the Eastern Anatolian Volcanic Province (EAVP) are significant sources of volcanic ash (tephra), which are found in palaeoclimatic and archaeological records in the eastern Mediterranean region. However, there is sparse glass geochemistry and little known about the eruption history of these volcanoes, limiting their full tephrochronological potential. Here, we present detailed, comprehensive singleshard major, minor and trace elem geochemistry of tephra deposits sampled at new and previously studied proximal outcrops around Lake Van and fourteen visible tephra layers (V-layers) from the ICDP Ahlat Ridge (AR) core of Lake Van spanning 130 to 30 ka. The volcanic glass from the following proximal eruption units: Lower Trachytic Pumice (LT-P), Lower Trachytic Ignimbrite (LT-I), Middle Pumices, Upper Rhyolitic Pumice and Ignimbrite (UR-PI), Upper Trachytic Ignimbrite (UT-I), and the chosen V-layers were geochemically characterised. This new glass data allows new and revised previous chrono-stratigraphic correlations between the proximal units and several V-layers. Mixed rhyolitic and trachytic glasses of V-18a correlate to the UR-P and UR-I proximal tephra units, and to previously published data from the Middle Nemrut (M-NF)-O, M-NF-I, Tatvan Ignimbrite and AP-8 units. These are all from the same caldera forming eruption of Nemrut at similar to 33 ka. Glasses of the older V-30 layer correlate to a Middle Pumice Unit and M-NF-R, and V-45 represents the 'Cekmece Formation'. The trachytic glasses of V-51 correlate to LT-P, LT-I and the M-NF-Agglutinate unit erupted from Nemrut. The distinctive basaltic glasses from V-60 correlate to an eruption of.Incekaya and V-64 is a newly identified eruption from the Suphan volcano. The older V-layers identified and analysed are from Nemrut based on comparing the new glass compositions to previously published whole-rock and glass data. This comparison indicates the V-75 pantelleritic tephra correlates to the dated AP-4 proximal unit. Each of these large eruptions are easily chemically differentiated using SiO2, FeOt, CaO and Al2O3. The integration of the proximal outcrops with the continuous, well-constrained Lake Van sedimentary medial record provides a detailed tephrostratigraphic record in a volcanic region where the proximal outcrop record is fragmented and confusing.
Nemrut Kalderasının Mineralojik-petrografik Karakteristikleri ve Tektonizma-volkanizma İlişkilerinin İncelenmesi
(2003) Karaoğlu, Özgür; Tolluoğlu, Arif Ümit; Ozdemir, Yavuz
Bölgesel sıkışmalı-gerilmeli tektono-volkanik rejim ürünü kaldera sistemlerinden birisi olan Nemrut Stratovolkanı, Doğu Anadolu'da kuzey-güney yönlü açılmayla başlayan, volkanizma sürecinin karakteristik en genç üyesidir. Nemrut Stratovolkanı, Bitlis ili Tatvan ilçesinin 15 km kuzey batısında yer almakta olup kaldera taban alanı yaklaşık 36 km2 dir. Kaldera öncesi evre yaklaşık kuzey-güney yönlü çatlaklardan, ikincil çıkış noktalarından ve Stratovolkana ait ana bacadan yer yüzüne ulaşan lavlar ve piroklastik türevler ile temsil edilmektedir. Kaldera öncesi evrede meydana gelen volkanik ürünler K-G, KD-6B, KB-SD yönlü açılma çatlakları ve KD-GB doğrultulu sol yönlü, KB-SD doğrultulu sağ yönlü doğrultu atımlı faylara bağlı olarak yüzeylemişlerdir. Kaldera öncesi evrenin ilk ürünleri Bitlis Vadisi içerisindeki bazaltik lav ve trakitik ignimbirit akıntısı ile Kaldera kuzeybatısında yüzeylenen trakitik ve bazaltik lav çıkışları olarak ayırtlanmıştır. Bazaltik lavlar Bitlis Vadisi'ni tamamen doldurmuş ve Baykan ilçesine kadar ulaşmıştır. Nemrut Volkanizmasına ait ilk bazaltik lavlar (effüzif) düşük enerjilidir. Lav akıntılarında 25-30 m. kalınlığa ulaşan blok yapısı 'Hawaii T/p' volkanizmalara özgü Aa tipi lavları karakterize etmektedir. Trakitik ignimbiritik akış ise yüksek enerjili patlamalar (eksplozif) sonucu oluşmuştur. Kaldera kuzeybatısında yüzeylenen trakitik lav çıkışları orta enerjili (ekstrüzif), bazaltik lav çıkışları ise blok yapısı gösterir. Büyük miktarlarda volkanik malzeme püskürten Nemrut Volkanı, daha sonraki evrede koni oluşum aşamasını tamamlayarak yeni bir sürece girmiştir. Yaklaşık 800 metrelik bir kısmın içe çöktüğü tahmin edilmektedir. Jeolojik süreç içinde Stratovolkanın bir süre suskunluk dönemi geçirdiği daha sonra tekrar aktivitesini sürdürdüğü anlaşılmaktadır. Bu süreç esnasında lav ve piroklastik ürünler gelişmiştir. Kaldera oluşumunu takiben eden evrede krater gölü ile magma etkileşimi ürünü 'hidrovolkanik püskürmeler1 meydana gelmiştir. Bol gaz boşluklu vitrofir riyolit lav çıkışları, piroklastik yayılım oluşumları bu sürece ait volkanik ürünlerdir. Kaldera kuzeyinde yer alan Nemrut Kırığına bağlı volkanik etkinlik devam etmiş ve parazitik bir koni oluşmuştur. Daha sonra koni üzerindeki küçük ölçekli göçük küçük bir krater şeklinde gelişmiştir. Bu püskürmenin ardından vitrofir riyolit lavlar çıkış yaparak parazitik koni gelişimini tamamlamıştır. Açılma çatlağı üzerinde ve parazitik koni çevresinde bilinen en son lav akışları meydana gelmiştir. Bu lavlar düşük enerjili' (effüzif) Aa tipi lav akışlarıdır. Patlama daha çok 'Fissiir Tip' volkanik etkinlik olarak gözlenir. Stratovolkana ait tüm lavlarda porfirik doku yaygındır. Sanidin asit karakterli tüm lavlarda değişmez mineraldir. Olivin fenokristalleri bazaltik kayaçlarda, klinopiroksenler bazaltik ve trakiandezitik kayaçlarda, amfibol ve biyotit mineralleri ise trakitik ve riyolitik kayaçlarda yaygın olarak gözlenmektedir. Kaldera duvarlarında yer alan trakit karakterli lavlarda ise yaygın olarak kuvars mineralleri gözlenmektedir.
New Palaeolimnological Record From West Anatolia (paleo-Kuleonu Lake) Provides New Information on the Activity of the Golcuk Volcanism and the Distribution of the Santorini Minoan Eruption
(Wiley, 2025) Senkul, Cetin; Unlu, Yasemin; Ozdemir, Yavuz; Kadioglu, Yusuf Kagan; Guerboga, Sule
Anatolia, which had active volcanoes during the Pleistocene and Holocene periods, was also influenced by volcanic eruptions around the Eastern Mediterranean. Therefore, tephrochronology is an important research topic in palaeoenvironmental studies conducted in Anatolia. This study focuses on the geochemical characteristics, chronologies and source areas of six different tephra layers identified in a 16 m sediment core obtained from Paleo-Kuleonu Lake in the Lake District of West Anatolia. Whole-rock geochemistry is used to determine the geochemical characteristics and source of the tephra layers, micro X-ray fluorescence analysis is used to determine relative element changes throughout the cores, and C-14 analysis is performed to establish the chronologies. The geochemistry of the Paleo-Kuleonu Lake tephra layers is consistent with the Golcuk volcanism located in West Anatolia province and the Minoan eruption within the Aegean volcanic province. The layers that resemble the geochemistry of the Golcuk volcanism accumulated at similar to 33 218 cal a BP (PLK-19-1; 30 cm), similar to 32 267 cal a BP (PLK-19-2: 18 cm), similar to 31 597 cal a BP (PLK-19-3; 8 cm), similar to 31 300 cal a BP (PLK-19-4; 17 cm) and similar to 26547 cal a BP (PLK-19-5; 13 cm) and are associated with the last eruptive cycle (Cycle III) of the volcanism. The closest tephra layer to the surface in the sediment core, designated as PLK-19-6 (similar to 1.5 cm), shows geochemical similarities with the Santorini Minoan eruption. However, according to our data, the age of the tephra layer is similar to 4717 BP/similar to 5542 cal a BP, which is inconsistent with the widely accepted date for the Minoan eruption in the literature. The discrepancy between the geochemical match and chronological inconsistency is discussed in the context of the results presented in the paper. (c) 2025 John Wiley & Sons, Ltd.
Origin and Petrogenesis of Magmatism in Collision-Related Environments: Evidence From the Melikler Volcanics on the Kars Plateau-Turkey in the Turkish-Iranian High Plateau
(Oxford Univ Press, 2023) Oyan, Elif; Oyan, Vural; Ozdemir, Yavuz; Gulec, Nilgun
The temporal distribution of enriched source components and magmatism in continental collision zones provides critical information about mantle dynamic processes in collision-related environments. This paper presents petrology, mineralogy, K-Ar ages and whole-rock major and trace elements, as well as Sr-Nd-Pb-Hf isotopic compositions of Melikler volcanism in Kars Plateau (KP) in the East Anatolia Collision Zone, NE Turkey, with the aim to understand the role of the subducting slab, the origin of magmatism and the geodynamic evolution in the collision-related environments. Our K-Ar dating results show the Melikler volcanism erupted between 5.29 and 1.7 Ma and allows us to divide it into an early (5.29-2.53 Ma) and a late (2.24-1.7 Ma) stage. Major-trace element abundances, isotopic compositions, EC(R) AFC (energy-constrained recharge, assimilation, and fractional crystallisation) and MELTS model calculations of both stages indicate that the least evolved samples were not affected by significant crustal contamination and fractional crystallisation. More evolved samples of the late stage underwent AFC processes with up to 6-9% crustal assimilation; however, those of the early stage were differentiated from a parental magma composition via AFC (up to 2-7.5% crustal assimilation) and experienced magma replenishment at pressure of 0.5 kbar; thus, both early and late stages have experienced open system conditions. The least evolved samples of both stages across the KP have arc-enriched geochemical and isotopic signatures, characterised by prevalent negative Nb-Ta anomalies and moderately radiogenic Sr, unradiogenic Nd-Hf and highly radiogenic Pb isotopic compositions. These primary melts could be derived from a depleted MORB mantle source metasomatised by sediment melt from the subducting Neotethys oceanic slab. Combined trace elemental and isotopic modelling results suggest that the least evolved samples of the early stage were formed by 2-4% melting of an amphibole-bearing garnet lherzolitic mantle source, which was metasomatised by 0.3-0.5% contribution of subducted slab component with a ratio of sediment melt/AOC (altered oceanic crust) melt about 90:10. A depleted lherzolitic mantle source containing apatite and garnet through inputs of 0.6-0.8% melts derived from the subducted oceanic slab, with 5-10% partial melting degree, could produce the least evolved samples of the late stage. Thermobarometric calculations reveal that the least evolved samples of the late stage are derived from the lithosphere-asthenosphere boundary at a depth of 77-82 km; in contrast, those of the early stage are produced from the lithosphere at a depth of 66-69 km. Literature data and the findings obtained from this study indicate that the onset of the Arabian-Eurasian collision may have occurred in the Oligocene and lithospheric dripping caused by the hard collision that occurred around the Late Miocene-Early Pliocene may produce the Melikler volcanic rocks.
Petrogenesis of Middle Miocene To Early Quaternary Basalts From the Karayaz?-G?ksu Plateau (Eastern Anatolia, Turkey): Implication for the Role of Pyroxenite and Lithospheric Thickness
(Elsevier, 2022) Ozdemir, Yavuz; Oyan, Vural; Jourdan, Fred
In Eastern Anatolia, the Karayazi-Go center dot ksu basaltic plateau is one of the basaltic eruption centers of post-collisional volcanism, located between the convergence zone of the Arabian and Anatolian plates. The geological and geochemical evolution of the plateau is documented using new 40Ar/39Ar age data, major-and trace element abundances, mineral geochemistry, and isotope compositions (Sr-Nd-Hf) for better understanding the petrogenesis and mantle source characteristics. Samples yield whole-rock 40Ar/39Ar ages of 12.53 +/- 0.05 and 12.68 +/- 0.05 Ma for transitional basalts (Middle Miocene), 5.88 +/- 0.20 Ma for tholeiitic lavas (Late Miocene), and 2.28 +/- 0.03 and 2.48 +/- 0.12 Ma for alkali members (Early Quaternary). The results suggest that the fractional crystallization of olivine and clinopyroxene in transitional, tholeiitic and lower alkaline lavas, and clinopyroxene in upper alkaline lavas, played a crucial role in their magmatic evolution without significant crustal contamination. Clinopyroxene-liquid equilibria indicate that the crystallization of transitional basalts occurred at the Moho and lower crust (temperature range 1157-1215 degrees C), tholeiitic basalts at the lower crust (temperature range 1154-1195 degrees C), alkaline basalts at lower to mid-crustal depths (temperature range 1083-1195 degrees C). The subduction-related metasomatism is in the form of melts derived from subducted sediments and decrease from Middle Miocene transitional to alkaline Early Quaternary basalts, as indicated by the Sr-Nd-Hf isotopes and Ba/ La and Th/Yb contents. The Early Quaternary alkaline basalts contain contributions from isotopically depleted but chemically enriched (enriched-MORB-like) asthenospheric mantle domain. Major elements-based parameters and olivine mineral chemistry yield that Karayazi-Go center dot ksu basalts could not be derived from a sole peridotite mantle source; the pyroxenite/eclogite-like mantle component would have contributed to the members of the plateau. Three-component mixing results using Sr-Nd isotopes indicate that the altered oceanic crust contributes to 0.5%-1% of the melt (crust vs. sediment about 65:35) for tholeiitic and alkaline basalts and reach up to 4% for transitional basalts (crust vs. sediment about 55:45). Melt equilibration depths of the basalts indicate that the lithospheric thickness of the region has not been changed on a large scale since the Middle Miocene to the Early Quaternary.
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.
Volcano Stratigraphy and Petrogenesis of the Nemrut Stratovolcano (East Anatolian High Plateau): the Most Recent Post-Collisional Volcanism in Turkey - Reply
(Elsevier, 2007) Ozdemir, Yavuz; Karaoglu, Ozguer; Tolluoglu, Arif Umit; Gulec, Nilgun