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2. 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.

Author

Oyan, Elif, Oyan, Vural, Özdemir, Yavuz, and Güleç, Nilgün

Subjects
*VOLCANOLOGY, *ADAKITE, *MAGMATISM, *PETROGENESIS, *OCEANIC crust, *VOLCANIC ash, tuff, etc.
Abstract

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. [ABSTRACT FROM AUTHOR]

Published
2023
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5. Melikler bazaltlarının petrolojisi: Kars platosu üzerindeki bazaltik volkanizmanın magmatik evrimi

Author

Oyan, Elif, Özdemir, Yavuz, and Jeoloji Mühendisliği Anabilim Dalı

Subjects
Jeoloji Mühendisliği, Geological Engineering
Abstract

Bu tez çalışmasında, Kars Platosu üzerindeki çarpışmayla ilişkili Melikler bazaltik volkanizmasının petrolojik evrimi detaylı olarak sunulmuştur. Elde edilen K-Ar yaş verileri magmatik aktivitenin 4.1 ile 1.7 My aralığında oluştuğuna işaret eder. Volkanik ürünler bazalttan andezite kadar değişen kompozisyonlarda, alkali ve subalkali lavlardan meydana gelir. Lav serilerinin tamamı olivin, piroksen, plajiyoklaz ve oksit fenokristalleri ve mikrolitlerinden oluşurlar ve intersertal, hyalopilitik ve vitrofirik dokular sergilerler.FC (fraksiyonel kristallenme), AFC (asimilasyonla birleşik fraksiyonel kristallenme) ve EC-RAFC (enerjiye bağımlı fraksiyonel kristallenme, asimilasyon ve magma tazelenmesi) model hesaplamaları Melikler bazaltik volkanizmasının evriminde fraksiyonel kristallenme, magma tazelenmesi ve kıtasal kirlenmenin önemli rol oynadıklarına işaret eder. En az evrimleşmiş bazaltik lavlarda, büyük iyon yarıçaplı litofil elementlerin (BİYE) ve hafif nadir toprak elementlerin (HNTE) yüksek alan şiddetli elementlere (YAŞE) göre belirgin zenginleşmesi, yüksek 87Sr/86Sr, Pb ve düşük 143Nd/144Nd ve 177Hf/176Hf izotopik oranları, Melikler bazaltik volkanizmasının manto kaynak alanının baskın olarak akışkanlardan ziyade sediman ergimeleri ile zenginleştiğine işaret eder. Kısmi ergime model hesaplamaları platonun bu parçasındaki bazaltik ergiyiklerin kısmi ergime derecesi %0.4 ile %4 arasında değişen ve amfibol ile granat içeren metasomatize olmuş manto kaynağının ergimesi ile üretilebileceğini göstermiştir. In this thesis, petrologic evolution of the collision-related Melikler basaltic volcanism on the Kars Plateau (Eastern Anatolia, Turkey) is presented in detail. The obtained K-Ar dating results indicate that this magmatic activity occurred between 4.1 and 1.7 Ma. Volcanic products consist of alkaline to sub-alkaline lavas, ranging in their compositions from basalt to andesite. All of the lava series composed of olivine, pyroxene, plagioclase and oxide phenocrystals and microlites, displaying intersertale, hyalopilitic and vitrophyric textures. FC (fractional crystallisation), AFC (assimilation combined fractional crystallisation) and EC-RAFC (Energy-constrained assimilation, fractional crystallisation and magma recharge) model calculations suggest that fractional crystallisation, magma replenishment and crustal contamination processes play an important role in the evolution of the Melikler basaltic volcanism. Enrichment of large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to high strength field elements (HFSE) and higher 87Sr/86Sr, Pb and lower 144Nd/143Nd and 176Hf/177Hf of the least evolved basaltic samples indicate that the mantle source region of the Melikler basaltic volcanism might be enriched by melts that were derived from subducted sediments rather than from fluids. Partial melting model calculations show that basaltic melts in this part of the region might have been produced by melting of a metasomatised mantle source containing both amphibole and garnet with a partial melting degree between 0.4 and 4%. 118

Published
2018

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