Kaygusuz, Abdullah; Aslan, Zafer; Aydınçakır, Emre; Yücel, Cem; Gücer, Mehmet Ali; Şen, Cüneyt

This paper presents Sr-Nd-Pb isotopic and whole-rock geochemical data of Miocene to Pliocene volcanic rocks in the Eastern Anatolia (Turkey) aiming to unravel their sources and evolutionary history. The wide compositional range of lavas and pyroclastics includes basaltic andesite, basaltic trachyandesite, trachyandesite, andesite and trachydacite. These calc-alkaline volcanics are enriched in large ion lithophile elements and light rare earth elements and depleted in the high field strength elements. Sr-Nd isotope data indicate low values for 87Sr/86Sr(i) (0.70432–0.70464) and high values for 143Nd/144Nd(i) (0.51272–0.51282). Further, these data are within the mantle array of the isotope ratio diagram. The lead (Pb) isotopic compositions (206Pb/204Pb(i) = 18.33 to 18.62, 207Pb/204Pb(i) = 15.51 to 15.60, 208Pb/204Pb(i) = 38.10 to 38.45) reveals the presence of an enriched source. The main petrological processes involved fractional crystallization and the mixing of at least two fractionated magmas having same source characteristics. All evidence supports the findings that the Kandilli volcanic rocks were derived from a partial melting of the both spinel and garnet bearing subcontinental lithospheric mantle, which had been previously metasomatized by mostly fluids derived from subducted slab during the collisional and post-collisional extension-related geodynamic setting in the Eastern Anatolia region of Turkey.

Yücel, Cem; Aydınçakır, Emre; Akaryali, Enver; Gücer, Mehmet Ali

Doğu Pontid orojenik kuşağında (KD Türkiye) farklı magma türleri altında oluşmuş farklı volkanikkayaçlar yüzeyleme vermektedir. Tersiyer volkanizması, Gümüşhane ve çevresinde asidik, nötr vebazik volkanik ve piroklastik kayaçlardan meydana gelmektedir. Bu volkanizma doğu Pontidler'inevriminde ise önemli bir rol oynamaktadır. Bu çalışma kapsamında Altınpınar (Torul/Gümüşhane)civarında yüzeyleme veren Tersiyer yaşlı hornblendli andezitik kayaçların petrografisi, mineralkimyası ve sıcaklık-basınç koşulları irdelenmiştir. Andezitler başlıca hornblend (amfibol),plajiyoklas (An40-61Ab38-57Or1-5), klinopiroksen (Wo44-45En43-44Fs12) ve opak (genellikle magnetit vepirit) mineralleri, ikincil kil, serizit, kalsit ve klorit mineralleri içerir ve mikrolitik-porfirik vevitrofirik porfirik dokular sergiler. Bazı hornblend mineralleri iri kristalli gelişmiş olup, plajiyoklasve opak mineral kapanımları içermektedir. Tüm hornblendler CaB >= 1.5, (Na+K)A <0.5 ve CaA <0.5parametrelerine sahip kalsik tip olup, magnezyohornblend bileşimi sunmakta, Mg# (Mg/Mg+Fe2+)ise 0.72-0.91 arasında değişmektedir. Andezitlerde kalsik amfibol jeotermobarometri denklemlerinikullanarak hesaplanan tahmini jeotermometre (T), jeobarometre (P) ve oksijen fugasitesi (?O2/ ?NNO) değerleri sırasıyla 765 - 867 °C (ort= 790±20 °C); 2.5 - 4 kbar ve -14.4 ile -11.1 olarakhesaplanmıştır. Elde edilen bu değerler hornblendlerin kıtasal kabukta 9 - 15 km derinliklerdekristallendiğini işaret etmektedir. Minerallerin kimyasal özellikleri inceleme alanındaki andezitlerinkalk-alkali bir ana magmadan itibaren kristallenmiş olduğunu göstermektedir.

Yücel, Cem

Doğu Pontid Orojenik Kuşağında Akçaabat (Trabzon) güneyi ve çevresinde yüzeyleme veren Kampaniyen yaşlı volkanik kayaçlar; bazalt, bazaltik andezit ve andezit bileşiminde olup, petrografik olarak klinopiroksen , plajiyoklas (An80-84), olivin ve opak minerallerden oluşurlar. Tüm kayaç hamurunda uygulanan 40Ar-39Ar yaşlandırma metoduyla volkanitlerin yaşları 82.61±0.34 My (Üst Kretase, Kampaniyen) olarak belirlenmiştir. Volkanitler kalk-alkalen karaktere sahiptirler. İlksel manto (İM)'ya normalize edilmiş iz element değişim diyagramlarında büyük iyon yarıçaplı litofil element (BİLE; Sr, K2O, Rb, Ba), Th ve Ce bakımından zenginleşme, Zr, Y, Nb, Ta ve TiO bakımından fakirleşme ile karakterize edilen yitim imzasına sahiptirler. Ayrıca, kondrite normalize edilmiş nadir toprak element (NTE) dağılımları, kayaçların düşük-orta derecede zenginleştirklerini göstermiştir (LaN/LuN=2-3.4). Volkanitlerin ana magmasının gelişiminde fraksiyonel kristallenmenin rolü magma karışımı ve asimilasyonfraksiyonel kristalleşmeye (AFC) göre daha etkindir. Tüm bu veriler ışığında Kampaniyen yaşlı volkanitlerin ana magmasının yitim etkisiyle, daha çok akışkanlar tarafından metazomatizmaya uğratılmış spinel lerzolitik bileşimdeki zenginleşmiş bir kaynaktan türediği ve daha sonra kabuk içerisinde özellikle fraksiyonel kristallenme ve daha az oranda da magma karışımı gibi magmatik olayların etkisiyle geliştiği düşünülmektedir

Yücel, Cem; Arslan, Mehmet; Temizel, İrfan; Abdioğlu Yazar, Emel; Ruffet, Gilles

The Eocene and Miocene volcanic rocks between the cities of Trabzon and Giresun in the Eastern Pontides (NE Turkey) erupted as mildly and moderately alkaline magmas ranging from silica-saturated to silica-undersaturated types. 40Ar-39Ar dating and petrochemical data reveal that the studied volcanic rocks are discriminated in two: Lutetian (Middle Eocene) mildly alkaline, (basaltic rocks: 45.31 ± 0.18 to 43.86 ± 0.19 Ma; trachytic rocks: 44.87 ± 0.22 to 41.32 ± 0.12 Ma), and Messinian (Late Miocene) moderately alkaline volcanic rocks (tephrytic rocks: 6.05 ± 0.06 and 5.65 ± 0.06 Ma). The trace and the rare earth element systematic, characterised by moderate light earth element (LREE)/heavy rare earth element (HREE) ratios in the Eocene basaltic and trachytic rocks, high LREE/HREE ratios in the Miocene tephrytic rocks, and different degrees of depletion in Nb, Ta, Ti coupled with high Th/Yb ratios, show that the parental magmas of the volcanic rocks were derived from mantle sources previously enriched by slab-derived fluids and subducted sediments. The Sr, Nd and Pb isotopic composition of the Eocene and Miocene volcanic rocks support the presence of subduction-modified subcontinental lithospheric mantle. During the magma ascent in the crust, parental magmas of both the Eocene and Miocene volcanic rocks were mostly affected by fractional crystallisation rather than assimilation coupled with fractional crystallisation and mixing. The silica-undersaturated character of the Miocene tephrytic rocks could be attributed to assimilation of carbonate rocks within shallow-level magma chambers. The parental magmas of the Eocene volcanic rocks resulted from a relatively high melting degree of a net veined mantle and surrounding peridotites in the spinel stability field due to an increase in temperature, resulting from asthenospheric upwelling related to the extension of lithosphere subsequent to delamination. The parental magmas for the Miocene volcanic rocks resulted from a relatively low melting degree of a net veined mantle domain previously modified by metasomatic melts derived from a garnet peridotite source after decompression due to extensional tectonics, combined with strike-slip movement at a regional scale related to ongoing delamination.

Temizel, Irfan; Arslan, Mehmet; Yücel, Cem; Abdioğlu, Emel; Ruffet, Gilles

40Ar-39Ar age, whole-rock chemical, and Sr-Nd isotope data are presented for the post-collisional, Eocene (51.3-44.1 Ma)-aged volcanic rocks from the Bafra (Samsun) area in the western part of the Eastern Pontides (N Turkey) aiming to unravel their sources and evolutionary history. The studied Eocene volcanic rocks can be divided into two groups: analcime-bearing (tephritic lava flows and dykes) and analcime-free (basaltic to trachytic lava flows and basaltic dykes). The analcime-bearing volcanic rocks have a fine-grained porphyritic texture with clinopyroxene phenocrysts, whereas analcime-free volcanic rocks show a variety of textures including hyalo-microlitic microgranular porphyritic, intersertal, trachytic, fluidal, and glomeroporphyritic. The volcanic rocks also show evidence of mineral-melt disequilibrium textures such as sieved, rounded, and corroded plagioclases, partially melted and dissolved clinopyroxenes and poikilitic texture. Petrochemically, the parental magmas of the volcanic rocks evolved from alkaline to calc-alkaline lava suites and include high-K and shoshonitic compositions. They display enrichments in light rare earth and large ion lithophile elements such as Sr, K, and Rb, as well as depletions in high field strength elements such as Nb, Ta, Zr, and Ti, resembling subduction-related magmas. The analcime-bearing and -free volcanic rocks share similar incompatible element ratios and chondrite-normalised rare rearth element patterns, indicating that they originated from similar sources. They also have relatively low to moderate initial 87Sr/86Sr (0.7042-0.7051), high positive εNd(t) values (+0.20 to +3.32), and depleted mantle Nd model ages (TDM1 = 0.63-0.93 Ga, TDM2 = 0.58-0.84 Ga). The bulk-rock chemical and Sr-Nd isotope features as well as the high Rb/Y and Th/Zr, but low Nb/Zr and Nb/Y ratios, indicate that the volcanic rocks were derived from a lithospheric mantle source that had been metasomatised by slab-derived fluids. Trace element modelling suggests that the parental magma(s) of the volcanic rocks represent mixtures of melts derived by low-degree (~5-10%) partial melting of spinel-lherzolite (40-85%) and garnet-lherzolite (15-60%) mantle sources. Sr-Nd isotopic modelling also suggests that a 25-35% lower crustal component was added in the parental magmas; AFC modelling additionally indicates minor upper crustal contamination during the evolution of the volcanic rocks. In conclusion, integration of the geochemical, petrologic, and isotopic data with regional geology suggests that the analcime-bearing and -free volcanic rocks evolved from parental magma(s) derived from melts of a subcontinental lithospheric mantle and lower crustal sources.

Temizel, İrfan; Arslan, Mehmet; Abdioğlu, Emel; Yücel, Cem

Monzogabbro stocks including felsic enclaves (monzosyenite) around the Bafra (Samsun) area at the western edge of the Eastern Pontides cut Eocene-aged volcanic and sedimentary units. The monzogabbros contain plagioclase, alkali feldspar, clinopyroxene, olivine, hornblende, biotite, apatite, and iron-titanium oxides, whereas the felsic enclaves contain alkali feldspar, plagioclase, hornblende, biotite, clinopyroxene, and iron-titanium oxides. Mineral chemistry data suggest that magmas experienced hydrous and anhydrous crystallization in deep and shallow crustal magma chambers. Several thermobarometers were used to estimate temperatures of crystallization and emplacement for the mafic and felsic magmas. Clinopyroxene thermobarometry yielded 1100-1232 C and 5.9-8.1 kbar for monzogabbros, and 931-1109 C and 1.8-6.9 kbar for felsic enclaves. Hornblende thermobarometry and oxygen fugacity estimates reveal 739-971°C, 7.0-9.2 kbar and 10−9.71 for monzogabbros and 681-928°C, 3.0-6.1 kbar and 10−11.34 for felsic enclaves. Biotite thermobarometry shows elevated oxygen fugacity varying from 10−18.9-10−11.07 at 632-904°C and 1.29-1.89 kbar for monzogabbros, to 10−15.99 -10−11.82 at 719-873°C and 1.41-1.77 kbar for felsic enclaves. The estimated zircon and apatite saturation temperatures are 504-590°C and 693-730°C for monzogabbros and 765-775°C and 641-690°C for felsic enclaves, respectively. These data imply that several phases in the gabbroic and syenitic magmas did not necessarily crystallize simultaneously and further indicate that the mineral compositions may register intervals of disequilibrium crystallization. Besides, thermobarometry contrasts between monzogabbro and felsic enclave may be partly a consequence of extended interactions between the mafic and felsic magmas by mixing/mingling and diffusion. Additionally, the hot felsic magma was close to liquidus conditions (crystallinity < 30%) when injected into cooler mafic magma (crystallinity > 50%), and thus, the monzogabbro stocks reflect hybrid products from the mingling and incomplete mixing of these two magmas.

Yücel, Cem; Temizel, Irfan; Abdioʇlu, Emel; Arslan, Mehmet; Yaʇcioʇlu, Ufuk Celal

Silica-undersaturated mafic volcanic rocks of Tertiary age in form of lava flows, dikes and sills of tephritic compositions extend along the northern part of the Eastern Pontides. These rocks typically contain Ca-clinopyroxene (Wo32-53En26-54Fs8-24), analcime, Fe-Ti oxides, apatite and minor olivine, plagioclase (An49 - 94), K-feldspar (Or29 - 66), hornblende and phlogopite in microgranular porphyritic, hyalo-microlitic porphyritic and glomeroporphyritic textures. Petrochemical features of the studied rocks, such as enrichment in LILE, depletion in Nb, Ta and Ti and moderate or high LREE/HREE ratios, provide strong evidence for melt production from a subduction-metasomatized lithospheric mantle. Besides, the rocks are characterized by their low K2O contents and low K2O/Na2O ratios as a result of analcimization. Analcime detected in these rocks appears to have formed by pseudomorphic mineral replacement reactions. Euhedral or anhedral analcime crystals, 100 - 600 um in diameter, are set in groundmass and display six-sided polygon or rounded shape and irregular cracks. The analcime pseudomorphs are colourless, milky white to grey and occur in clinopyroxene or in the groundmass. Based on the electron microprobe results, analcimes contain a minor amount of cations other than Na and probably represent the remnants of leucite as marked by K-zoning. X-ray diffraction studies of the analcime-bearing samples confirm the presence of cubic and tetragonal analcime crystals in addition to tetragonal leucite. The presence of Ca-clinopyroxene and plagioclase rather than their sodic equivalents, presence of anhydrous mineral phases and lack of Na differentiation trend as well as partial alteration of the rocks likely supports the secondary growth of analcime either during cooling or after magma solidification.