General Directorate of MTA

Ankara, Turkey

General Directorate of MTA

Ankara, Turkey
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Aydar E.,Hacettepe University | Schmitt A.K.,University of California at Los Angeles | Cubukcu H.E.,Hacettepe University | Akin L.,Hacettepe University | And 4 more authors.
Journal of Volcanology and Geothermal Research | Year: 2012

Episodes of high eruptive fluxes (>10 -3km 3/year) in continental environments are associated with magmatism related to subduction, post-orogenic collapse, intra-plate hot spots, or rifting. During such episodes, voluminous ignimbrite deposits are produced which cover landscapes over 10 4-10 5km 2. In such sequences, brief eruptive recurrence and chemical similarity limit the applicability of geochronological and geochemical correlation methods. Here, we present complementary geochronological data ( 40Ar/ 39Ar plagioclase eruption and 206Pb/ 238U zircon crystallization ages) for ignimbrites from the Miocene-Holocene Central Anatolian Volcanic Province (CAVP). In addition, we successfully employed zircon geochemistry (trace elements, oxygen isotopes) as an alteration-resistant indicator to correlate rhyodacitic to rhyolitic ignimbrites whose eruption age differences are too brief to be resolved by 40Ar/ 39Ar geochronology. By applying this method, we dismiss previous correlations between stratigraphic members (i.e., Sofular and Gördeles, Sofular and Saromadentepe), but demonstrate close relationships for other CAVP ignimbrites (i.e., Kavak units 1 to 4; Cemilköy ignimbrite and overlying fallout deposits). Our chronostratigraphy reveals two previously unrecognized eruptive pulses at ~9-8Ma and 7-5Ma which are characterized by increasing magmatic temperatures (~75-100°C within each cycle). Despite a long-term (10Ma) eruptive productivity that is about one order of magnitude smaller than in other magmatically active continental plateaus, the CAVP achieved high eruptive fluxes during brief (1-2Ma) intervals. © 2011 Elsevier B.V.

Uysal I.,Karadeniz Technical University | Ersoy E.Y.,Dokuz Eylül University | Dilek Y.,Miami University Ohio | Kapsiotis A.,Sun Yat Sen University | Sarifakioglu E.,General Directorate of MTA
Lithos | Year: 2016

The Eldivan ophiolite along the Izmir-Ankara-Erzincan suture zone in north-central Anatolia represents a remnant of the Neotethyan oceanic lithosphere. Its upper mantle peridotites include three lithologically and compositionally distinct units: clinopyroxene (cpx)-harzburgite and lherzolite (Group-1), depleted harzburgite (Group-2), and dunite (Group-3). Relics of primary olivine and pyroxene occur in the less refractory harzburgites, and fresh chromian spinel (Cr-spinel) is ubiquitous in all peridotites. The Eldivan peridotites reflect a petrogenetic history evolving from relatively fertile (lherzolite and cpx-harzburgite) toward more depleted (dunite) compositions through time, as indicated by (i) a progressive decrease in the modal cpx distribution, (ii) a progressive increase in the Cr#s [Cr / (Cr + Al)] of Cr-spinel (0.15-0.78), and (iii) an increased depletion in the whole-rock abundances of some magmaphile major oxides (Al2O3, CaO, SiO2 and TiO2) and incompatible trace elements (Zn, Sc, V and Y). The primitive mantle-normalized REE patterns of the Group-1 and some of the Group-2 peridotites display LREE depletions. Higher YbN and lower SmN/YbN ratios of these rocks are compatible with their formation after relatively low degrees (9-25%) of open-system dynamic melting (OSDM) of a Depleted Mid-ocean ridge Mantle (DMM) source, which was then fluxed with small volumes of oceanic mantle-derived melt [fluxing ratio (β): 0.7-1.2%]. Accessory Cr-spinel compositions (Cr# = 015-0.53) of these rocks are consistent with their origin as residual peridotites beneath a mid-ocean ridge axis. Part of the Group-2 harzburgites exhibit lower YbN and higher SmN/YbN ratios, LREE-enriched REE patterns, and higher Cr-spinel Cr#s ranging between 0.54 and 0.61. Trace element compositions of these peridotites can be modeled by approximately 15% OSDM of a previously 17% depleted DMM, which was then fluxed (β: 0.4%) with subduction-influenced melt. The Group-3 dunite samples contain Cr-spinel with elevated Cr#s (0.73-0.78) and low-TiO2 contents (<0.13 wt.%), implying higher degrees of melting (21-24%) of an already depleted DMM that was triggered by infiltration of low-Ti boninite melt with fluxing rates of 0.4-4.0%. The existence of interstitial, idiomorphic Cr-spinel (high Cr# and low Ti) in the Group-3 dunites is consistent with this interpretation. The occurrence of both MOR- and SSZ-type peridotites in the Eldivan ophiolite suggests that its heterogeneous upper mantle was produced as a result of different partial melting and melt-rock reaction processes in different tectonic settings within the Neotethyan realm. © 2016 Elsevier B.V.

Uysal I.,Karadeniz Technical University | Ersoy E.Y.,Dokuz Eylül University | Dilek Y.,Miami University Ohio | Escayola M.,National University of Salta | And 3 more authors.
Gondwana Research | Year: 2015

We present new whole-rock major and trace element, Re-Os isotope and mineral chemistry data for the upper mantle peridotites and mafic rocks in the Rehafiye ophiolite in NE Anatolia (Turkey), and discuss their significance for the mantle evolution in Neotethys. The Refahiye peridotites include clinopyroxene (cpx)-rich and cpx-poor harzburgites. Assuming an initial fertile mantle composition, the cpx-rich harzburgites have a limited range of Cr-spl Cr# (33-38), implying 14-18% melt extraction. However, TiO2 contents of the Cr-spl in these rocks are too high (up to 0.24wt.%) to explain their Ti concentrations with a simple melt extraction model in a mid-ocean ridge (MOR) setting, and suggest re-crystallization from an impregnating fertile melt. The interstitial phases of cpx in these samples have high TiO2 (up to 0.40wt.%) and Na2O (up to 0.25wt.%) contents. They also contain interstitial pargasitic amphibole with TiO2 contents varying between 0.69 and 0.88wt.%. These textures and the mineral chemistry data indicate refertilization of the previously depleted, MOR-type peridotites by percolating hydrous melts. The whole-rock REE partial melting modeling is consistent with slightly lower degrees of mantle melting (~12-14%) compared to the melt extraction degrees obtained from the Cr-spl compositions (~15%). Chromian spinel (Cr-spl) phases in the cpx-poor harzburgites show a wider variation of Cr#, ranging between 57 and 75, and reflect 30-40% of partial melting. In contrast, the whole-rock geochemistry of these rocks represents slightly lower degrees of partial melting, varying between 30 and 35%. The enrichment of TiO2 contents of the Cr-spl (up to 0.20wt.%) in some of the cpx-poor harzburgites can be explained by their interaction with Ti-rich hydrous melt formed at supra-subduction (SSZ) tectonic setting. Highly unradiogenic Os isotope composition (0.11956) of a cpx-poor harzburgite sample suggests an ancient melt depletion event experienced by these rocks, whereas its high Re content is a manifestation of subduction enrichment. The mafic units of the Refahiye ophiolite show MORB-like to island arc tholeiite (IAT) geochemical signatures typical of SSZ oceanic crust. A U-Pb zircon age of 183±1Ma obtained from an isotropic gabbro sample suggests that the crystallization of the SSZ-type mafic units in the Refahiye ophiolite is as old as the early Jurassic. © 2013 International Association for Gondwana Research.

Nicoll K.,University of Utah | Kucukuysal C.,General Directorate of MTA
Turkish Journal of Earth Sciences | Year: 2013

We present an overview of selected papers published since 2000 that interpret Late Quaternary multi-proxy palaeoclimate records from Turkey and the surrounding region of the Near-Middle East and Mediterranean region. Existing records in Turkey are rather limited in their resolution, and the locations studied thus far reflect a limited spatial and temporal distribution. Because Turkey is a very large country with numerous mountains that affect local weather conditions and create complex feedbacks, it is difficult to correlate trends across the broad landscape, and beyond. Published instrumental records are too short, and most palaeoclimate proxy records, including many lakes studied in Cappadocia and Konya, are low resolution. The Anatolian peninsula is sensitive to spatial and temporal shifts in the configuration, strength and persistence of global circulation patterns affecting the Mediterranean climate zone, including the mid-latitude westerlies, the continental climate system anchored over northern Asia and Siberia, and the Afro-Asian monsoonal system. As such, there is a strong need for additional new, high quality, well dated, and high-resolution multi-proxy records from more sites in Turkey. Deciphering the complexities of environmental change in central-interior and eastern regions of Turkey is particularly problematic, due to the paucity of published records. Additional observations of climate variability at the decadal-tocentennial scale are essential to better understand the ascendant controls on climate variation, the influence of rapid climate changes (RCCs) recognized in the marine record, and the causal mechanisms involved. Because the IPCC models forecast desiccation for Turkey and other drought-prone regions, it is particularly important to understand the natural baseline of hydroclimate variation across the broader Middle East and Mediterranean region. Additional study of past conditions has tremendous potential to inform the policy and practices of the future. © TÜBITAK.

Kucukuysal C.,General Directorate of MTA | Gunal Turkmenoglu A.,Middle East Technical University | Kapur S.,Cukurova University
Turkish Journal of Earth Sciences | Year: 2013

Palaeosols are very important in reconstructing palaeoclimate studies, since they are accepted as useful climate markers and as potential providers of proxy data. The study of the palaeosols of the Plio-Pleistocene rock sequences around Ankara revealed evidence for a reconstruction of the Quaternary palaeoclimate of the region. The study area is located in Bala, south-east of Ankara, which contains Middle Pleistocene red palaeosols with powdery to nodular calcrete developments, alternating with channel deposits. During this warm and arid period in the Pleistocene, the limited water available in the soil led to the accumulation of low magnesian carbonates, forming calcretes. The clay fractions of the samples were X-rayed using air-drying, ethylene-glycol solvation and heating treatments. The clay mineral contents were determined as smectite, kaolinite, illite and chlorite. Palygorskite was also identified. In the relative abundances of clay minerals, smectite, the most abundant clay mineral, is depleted towards the upper part of the section while the amount of palygorskite increases. Since palygorskite is the only pedogenic mineral formed during the Pleistocene, its presence can be accepted as evidence of the dominant arid climatic conditions. The isotopic composition of carbonates in the Bala section exhibits a slightly wider range in δ13C composition from -5.98‰ to -9.22‰ and a narrower range in δ18O composition from -7.19‰ to -8.66‰. The carbon isotope values clearly imply that arid to semiarid flora C4 is dominant, with C3:C4 mixed vegetation. This study suggests that the Middle Pleistocene is the time of the Mid-Brunhes Event when the dominantly warm climatic temperatures led to the development of calcretes in Bala, Ankara, as with all Quaternary Mediterranean-type calcretes. © Tübi̇tak.

Temiz U.,Bozok University | Savas F.,General Directorate of MTA
Arabian Journal of Geosciences | Year: 2015

The Akhüyük travertine mass crops out approximately 10 km to the north of Ereğli (Konya, Central Anatolia). Its morphology and relationship with the main controlling fault zones are investigated. The morhpological properties of six different fissure ridge travertines which make up the travertine mass are classified into four groups based on their geometrical properties and orientation. The fissure ridge travertines having a banded travertine thickness of 120 and 170 cm are considered as the oldest travertines in the study area. Sill-like structures and dilation are observed, indicative of the ongoing deformation after travertine precipitation. The height-to-width ratio of the fissure ridge travertines vary between 0.08 and 0.5. The morhological structures and parameters observed in the fissure ridge travertines are interpreted to stem from the low deformation rate in the study area. The relationship of the formation of the Akhüyük Fissure Ridge travertine with the Tuz Gölü (TGFZ) and Niğde fault zones (NFZ) is investigated. The TGFZ is determined to be the most significant structure that controls the Akhüyük fissure ridge travertines based on the extension direction determined, the location of the travertines, and the fact that the faults on the central and southeastern end of the TGFZ display the active normal fault zone with a right-lateral strike-slip component. © 2014, Saudi Society for Geosciences.

Antoine P.-O.,Montpellier University | Orliac M.J.,Montpellier University | Orliac M.J.,Royal Museum for Central Africa | Atici G.,General Directorate of MTA | And 7 more authors.
PLoS ONE | Year: 2012

Background: Preservation of fossil vertebrates in volcanic rocks is extremely rare. An articulated skull (cranium and mandible) of a rhinoceros was found in a 9.2±0.1 Ma-old ignimbrite of Cappadocia, Central Turkey. The unusual aspect of the preserved hard tissues of the skull (rough bone surface and brittle dentine) allows suspecting a peri-mortem exposure to a heating source. Methodology/Principal Findings: Here we describe and identify the skull as belonging to the large two-horned rhinocerotine Ceratotherium neumayri, well-known in the late Miocene of the Eastern Mediterranean Province. Gross structural features and microscopic changes of hard tissues (bones and teeth) are then monitored and compared to the results of forensic and archaeological studies and experiments focusing on heating effects, in order to reconstruct the hypothetical peri-mortem conditions. Macroscopic and microscopic structural changes on compact bones (canaliculi and lamellae vanished), as well as partial dentine/cementum disintegration, drastic enamel-dentine disjunctions or microscopic cracks affecting all hard dental tissues (enamel, cementum, and dentine) point to continued exposures to temperatures around 400-450°C. Comparison to other cases of preservation of fossil vertebrates within volcanic rocks points unambiguously to some similarity with the 79 AD Plinian eruption of the Vesuvius, in Italy. Conclusions/Significance: A 9.2±0.1 Ma-old pyroclastic density current, sourced from the Çardak caldera, likely provoked the instant death of the Karacaşar rhino, before the body of the latter experienced severe dehydration (leading to the wide and sustainable opening of the mouth), was then dismembered within the pyroclastic flow of subaerial origin, the skull being separated from the remnant body and baked under a temperature approximating 400°C, then transported northward, rolled, and trapped in disarray into that pyroclastic flow forming the pinkish Kavak-4 ignimbrite ~30 km North from the upper Miocene vent. © 2012 Antoine et al.

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