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Öğe C2/c pyroxene phenocrysts from three potassic series in the Neogene alkaline volcanics, NE Turkey: their crystal chemistry with petrogenetic significance as an indicator of P-T conditions(SPRINGER, 2009) Aydin, Faruk; Thompson, Richard M.; Karsli, Orhan; Uchida, Hinako; Burt, Jason B.; Downs, Robert T.Chemical and structural data are reported for C2/c pyroxene phenocrysts collected from three potassic series (Group A: basanite-tephrite, Group B: tephrite-phonolitic tephrite, Group C: alkaline basalt-trachybasalt) of the Neogene alkaline volcanics (NAVs) in northeastern Turkey, in order to investigate the evolution of the magmatic plumbing system and the location of magma chamber(s) with crystallization conditions. The rock series hosting the clinopyroxene phenocrysts show generally porphyritic texture and have a variable phenocryst-rich nature (20-58%), with phenocryst assemblages characterized by cpx +/- A ol +/- A plag +/- A foid +/- A amp +/- A bio. The clinopyroxene phenocrysts can be chemically classified as Ti- and Fe(3+)-rich Al-diopsides for Groups A and B (AB-cpxs) and Ti- and Fe(3+)-poor Al-diopsides for Group C (C-cpxs). They have poorly variable composition, clustering in the diopside field. Structurally, the diopside groups have nearly similar a (ranging from 9.73 to 9.75 A...), V (cell) (437.2-440.9 A...(3)), and a OE (c) beta > angle values (106.01A degrees aEuro"106.23A degrees), but some differences in polyhedral parameters and geometries of the AB-cpxs and C-cpxs have been observed. For example, the AB-cpxs are characterized by larger c (5.27-5.30 vs. 5.25-5.28 A...), V (T) (2.27-2.30 vs. 2.23-2.28 A...(3)), and V (M2) (25.53-25.72 vs. 25.41-25.59 A...(3)) values and smaller b (8.87-8.88 vs. 8.88-8.91 A...) and V (M1) (11.49-11.63 vs. 11.64-11.83 A...(3)) values with respect to the C-cpxs. In addition, the AB-cpxs show higher values of V (M2)/V (M1) (2.20-2.23) due to large V (M2) and small V (M1) compared to the V (M2)/V (M1) ratios of the C-cpxs (< 2.19). Such differences in the crystal structure of the AB-cpxs and C-cpxs from the NAVs are partly related to different crystallization pressures, but mostly related to variation in melt composition and, possibly, the influence of other crystallizing mineral phases. In particular, R(M2-O1) and R(M1-O2) (i.e. bond lengths) differences in the clinopyroxenes of different groups support the presence of evolved host rocks with different alkaline character (i.e. silica-undersaturated Groups A-B and silica-saturated Group C). Based on the cpx-geothermobarometry, the crystallization pressures for the C-cpxs are lower than 4.5 kbars, but the AB-cpxs have relatively high-pressure values (5.6-10.6 kbars), suggesting that the AB-cpxs crystallized in higher pressure environments. The relatively higher crystallization temperatures of the AB-cpxs also indicate higher cooling rates. The P-T estimates suggest that the source regions of the clinopyroxene phenocrysts from the NAVs were crustal magma chambers in a closed plumbing system at a moderate- to low-pressure regime.Öğe Compositional Variations, Zoning Types and Petrogenetic Implications of Low-pressure Clinopyroxenes in the Neogene Alkaline Volcanic Rocks of Northeastern Turkey(SCIENTIFIC TECHNICAL RESEARCH COUNCIL TURKEY-TUBITAK, 2009) Aydin, Faruk; Karsli, Orhan; Sadiklar, M. BurhanClinopyroxene phenocrysts and microphenocrysts in different series of the Neogene alkaline volcanic rocks from the eastern Pontides (NE Turkey) record various stages in the crystallization conditions and evolution history of the alkaline melt as well as its origin. Crystal chemical studies reveal that the clinopyroxenes in each rock series show strong textural and compositional similarities, which all reflect a common petrogenetic affinity. They have relatively high Mg-numbers (0.68-0.95), variable Al(2)O(3) (1.3-9.6 wt%), low TiO(2) (<2.7 wt%) and Na(2)O (<0.9 wt%) contents and low Al([6])/Al([4]) ratios (mostly <0.25), suggesting relatively low-pressure crystallization conditions of the magma in the storage region. The pressures calculated for the clinopyroxenes in each series are nearly similar and vary in the range of 2.4-4.6 +/- 0.9 kbars, which approximately corresponds to a crystallization depth of 714 +/- 3 km. The analyses of the compositional trends of the clinopyroxenes indicate the following types of zoning: (i) oscillatory and sectorial zoning related to melt crystallization (i.e. rapid cooling and crystallization), (ii) oscillatory, reverse zoning related to the different crystallization paths under a variable fluid regime, (iii) normal zoning related to the differentiation and fractional crystallization of the magma. Based on the primitive mantle- and chondrite-normalized trace and rare earth element patterns, all clinopyroxenes have high abundances of incompatible elements (i.e. La, Ce) with negative high field strength element anomalies (i.e. Zr, Ti) and low Nb/Y (0.1-0.2), Th/Y (<0.1) and Rb/Y (<0.03) ratios, suggesting derivation from a similar source. Obtained textural and mineral chemical data, as well as whole-rock compositions, thus suggest that the clinopyroxenes may have started to crystallize from alkaline basaltic magma derived from a homogeneous lithospheric mantle enriched by an earlier subduction event. After this process, the alkaline magma, from which early clinopyroxenes crystallized, underwent a relatively low-pressure fractional crystallization process. This was in closed magma chambers at different levels of the crust (or within a volcanic conduit system devoid of interaction processes), shown by variations in the different crystallization paths and in the fluid regime of the melt during differentiation and ascent of the magma, in a post-collisional extensional tectonic regime which affected the eastern Pontides during the Neogene.Öğe Contrasting complexities in the evolution of calc-alkaline and alkaline melts of the Nigde volcanic rocks, Turkey: textural, mineral chemical and geochemical evidence(E SCHWEIZERBARTSCHE VERLAGSBUCHHANDLUNG, 2008) Aydin, FarukThe Nigde volcanic province in central Turkey comprises four separate stratovolcanoes (Tepekoy, Cinarli, Melendiz and Keciboyduran) of Mio-Pliocene age (MPv) and several monogenetic cones of Pleistocene age (Pv). The MPv rocks are composed of large volume of andesitic lavas and pyroclastics with medium to high-K calc-alkaline character. They are strongly porphyritic with phenocryst assemblages of plag + opx + cpx + Fe-Ti oxides + bio +/- amph +/- quartz, and commonly exhibit disequilibrium textures such as complexly zoned plagioclases, reversely zoned pyroxenes, and reacted amphiboles and biotites. Geothermobaro-metric studies based on mineral chemistry data suggest that the MPv calc-alkaline magmas underwent a complex evolutionary history of cooling, crystallisation and mixing within two distinct magma chambers sited in the lower and in the upper crust, respectively. The rocks of Pv include small. volumes of alkaline basalts showing poorly porphyritic textures and equilibrated phenocryst assemblages of ol + cpx + lesser plag and Fe-Ti oxides. Textural features, and strong compositional variations in single phenocrysts from andesites clearly reflect magma mixing-mingling and open-system modifications. Major and trace element evidence also argues against dominant fractional crystallisation processes and supports magma mixing for andesitic magmas. In contrast, textural, mineral chemical and geochemical evidence for Pv alkaline rocks indicate that magmas had a relatively simple evolutionary history dominated by small degrees of fractional crystallisation of mafic minerals along volcanic conduits. MPv show typical island-arc trace element signatures, such as negative anomalies in high-field strength element (HFSE) and high ratios between HFSE and large ion lithophile elements (LILE). Slight HFSE negative anomalies are also observed in Pliocene alkaline basalt, suggesting contamination by arc component, either in the source or during alkaline magma ascent.Öğe Elemental and Sr-Nd-Pb isotopic geochemistry of the most recent Quaternary volcanism in the Erzincan Basin, Eastern Turkey: framework for the evaluation of basalt-lower crust interaction(ELSEVIER SCIENCE BV, 2008) Karsli, Orhan; Chen, Bin; Uysal, Ibrahim; Aydin, Faruk; Wijbrans, Jan R.; Kandemir, RaifWhole-rock geochemical and Sr, Nd and Pb isotope data are presented for a representative suite of the Quaternary Erzincan Volcanics (QEV) from the Erzincan basin (EB) along the North Anatolian Fault Zone, aiming to understand their origin and implications for basalt-lower crust interaction. Unspiked K-Ar and (40)Ar/(39)Ar dating of dome lavas from the QEVs yielded ages of 102 +/- 2 to 1061 +/- 88 ka. The QEVs range from high-K low silica trachy-andesite to rhyolite in composition, with rhyolite volumetrically the most abundant. All rocks show high-K calc-alkaline affinity, a geochemical signature common to many post-collisional magmas. They are characterized by enrichment in LILE (Rb, Ba, K, Th) and LREE ((La/Yb)(CN) = 3-33), with pronounced depletion of HFSE. All lavas show negligible or small negative Eu anomalies in the andesitic to dacitic and strong Eu anomalies in the rhyolitic samples. These rocks have relatively low (87)Sr/(86)Sr = 0.70404-0.70587 and slightly depleted Nd isotopic compositions (epsilon(Nd) from -0.9 to 2.8), with significantly varied Mg# ranging from 2 to 53. Pb isotopic compositions [(206)Pb/(204)Pb = 18.90-19.02, (207)Pb/(204)Pb = 15.64-15.70, (208)Pb/(204)Pb = 38.91-39.97] reveal an enriched source signature, which implies that some portions of metasomatized lithospheric mantle could have contributed to their genesis. The isotopic ratios and chemical features along with the textural and compositional disequilibrium of the plagioclases and amphiboles suggest that mixing of mafic and felsic magmas played an important role in the magma genesis. A possible scenario for the genesis of these volcanic rocks is that basaltic magma formed as a result of partial melting of a subcontinental lithospheric mantle source responding to a possible upwelling of asthenospheric mantle which was caused by the extension produced by strike-slip tectonics. Underplating of these high-temperature basaltic magmas sparked partial fusion of a juvenile lower continental crust producing felsic melts; then magma mixing between basaltic and the felsic magmas followed. Fractional crystallization, with minor amounts crustal contamination could have played an important role in the evolution of magma. Modelling based on Sr and Nd isotope data shows that less than 10% of a basic magma and about 90% of juvenile lower continental crustal material was involved in the generation of the QEVs in a pull-apart basin along the North Anatolian Fault Zone. (C) 2008 Elsevier B.V. All rights reserved.Öğe Generation of the Early Cenozoic adakitic volcanism by partial melting of mafic lower crust, Eastern Turkey: Implications for crustal thickening to delamination(ELSEVIER SCIENCE BV, 2010) Karsli, Orhan; Dokuz, Abdurrahman; Uysal, Ibrahim; Aydin, Faruk; Kandemir, Raif; Wijbrans, JanEarly Cenozoic (48-50 Ma) adakitic volcanic rocks from the Eastern Pontides NE Turkey consist of calc-alkaline and high-K calc-alkaline andesite and dacite, with SiO(2) contents ranging from 56 01 to 65 44 wt.%.. This is the first time that Early Eocene volcanism and adakites have been reported from the region. The rocks are composed of plagioclase, amphibole, quartz, and Mg-rich biotite. They have high and low-Mg# values ranging from 55 to 62 and 13 to 42. respectively. High-Mg# rocks have higher Ni and Co contents than low-Mg# samples. The rocks exhibit enrichments in large ion lithophile elements including the light rare earth elements, depletions in Nb, Ta and Ti and have high La/Yb and Sr/Y ratios. Their relative high I(Sr) (0.70474-0.70640) and low epsilon(Nd) (50 Ma) values (-2.3 to 0.8) are inconsistent with an origin as partial melts of a subducted oceanic slab. Combined major- and trace element and Sr-Nd isotope data suggest that the adakitic magmas are related to the unique tectonic setting of this region, where a transition from a collision to an extension stage has created thickening and delamination of the Pontide mafic lower crust at 50 Ma The. high-Mg adakitic magmas resulted from partial melting of the delaminated eclogitic mafic lower crust that sank into the relatively hot subcrustal mantle, and its subsequent interaction with the mantle peridotite during upward transport, leaving garnet as the residual phase, elevates the MgO content and Mg# of the magmas, whereas low-Mg# magmas formed by the melting of newly exposed lower crustal rocks caused by asthenospheric upwelling, which supplies heat flux to the lower crust. The data also suggest that the mafic lower continental crust beneath the region was thickened between the Late Cretaceous and the Late Paleocene and delaminated during Late Paleocene to Early Eocene time, which coincides with the initial stage of crustal thinning caused by crustal extensional events in the Eastern Pontides and rules out the possibility of an extensional regime before similar to 50 Ma in the region during the Late Mesozoic to Early Cenozoic. (C) 2009 Elsevier B.V. All rights reserved.Öğe Geochemical and Sr-Nd-Pb isotopic compositions of the Eocene Dolek and Sariqiqek Plutons, Eastern Turkey: Implications for magma interaction in the genesis of high-K calc-alkaline granitoids in a post-collision extensional setting(ELSEVIER SCIENCE BV, 2007) Karsli, Orhan; Chen, Bin; Aydin, Faruk; Sen, CueneytThe major and trace elements and Sr-Nd-Pb isotopes of the host rocks and the mafic microgranular enclaves (MME) gathered from the Dolek and Saricicek plutons, Eastern Turkey, were studied to understand the underlying petrogenesis and geodynamic setting. ne plutons were emplaced at similar to 43 Ma at shallow depths (similar to 5 to 9 km) as estimated from Al-in hornblende geobarometry. The host rocks consist of a variety of rock types ranging from diorite to granite (SiO2= 56.98-72.67 wt.%; Mg#= 36.8-50.0) populated by MMEs of gabbroic diorite to monzodiorite in composition (SiO2 = 53.21-60.94 wt.%; Mg#=44.4-53.5). All the rocks show a high-K calc-alkaline differentiation trend. Chondrite-normalized REE patterns are moderately fractionated and relatively flat [(La/Yb)(N)=5.11 to 8.51]. They display small negative Eu anomalies (Eu/Eu* =0.62 to 0.88), with enrichment of LILE and depletion of HFSE. Initial Nd-Sr isotopic compositions for the host rocks are epsilon(Nd)(43 Ma)= -0.6 to 0.8 and mostly I-Sr= 0.70482-0.70548. The Nd model ages (T-DM) vary from 0.84 to 0.99 Ga. The Ph isotopic ratios are ((206)pb/(204)pb)= 18.60-18.65, (Pb-207/Pb-204) = 15.61-15.66 and (Pb-208/Pb-204) = 38.69-38.85. Compared with the host rocks, the MMEs are relatively homogeneous in isotopic composition, with Is, ranging from 0.70485 to 0.70517, epsilon(Nd)(4 3 M a) -0.1 to 0.8 and with Pb isotopic ratios of (Pb-206/Pb-204)= 18.58-18.64, (Pb-207/Pb-204)= 15.60-15.66 and (Pb-208/Pb-204)=38.64-38.77. The MMEs have T-DM ranging from 0.86 to 1.36 Ga. The geochemical and isotopic similarities between the MMEs and their host rocks indicate that the enclaves are of mixed origin and are most probably formed by the interaction between the lower crust- and mantle-derived magmas. All the geochemical data, in conjunction with the geodynamic evidence, suggest that a basic magma derived from an enriched subcontinental lithospheric mantle, probably triggered by the upwelling of the asthenophere, and interacted with a crustal melt that originated from the dehydration melting of the mafic lower crust at deep crustal levels. Modeling based on the Sr-Nd isotope data indicates that similar to 77-83% of the subcontinental lithospheric mantle involved in the genesis. Consequently, the interaction process played an important role in the genesis of the hybrid granitoid bodies, which subsequently underwent a fractional crystallization process along with minor amounts of crustal assimilation, en route to the upper crustal levels generating a wide variety of rock types ranging from diorite to granite in an extensional regime. (c) 2007 Elsevier B.V All rights reserved.Öğe Magma interaction processes inferred from Fe-Ti oxide compositions in the Dolek and Saricicek plutons, Eastern Turkey(SCIENTIFIC TECHNICAL RESEARCH COUNCIL TURKEY-TUBITAK, 2008) Karsli, Orhan; Aydin, Faruk; Uysal, Brahim; Sadiklar, M. BurhanMagnetite-ulvospinel and ilmenite-hematite solid solution intergrowths from the high-K calc-alkaline Dolek and Saricicek plutons, Eastern Turkey, were investigated using microprobe analyses. Compositions of twenty-eight samples from the host rocks and their enclaves in the plutons were used to estimate the oxygen fugacity and temperature. The ilmenite and ulvospinel component exsolves out along certain preferred crystallographic planes in the titanomagnetite of the host rocks, while they are always absent in those of the mafic microgranular enclaves. The titanomagnetite and ilmenite show variations as Mt(98-70)Usp(02-30) and Ilm(99-65)Hm(01-35) in composition, respectively. Estimations of oxygen fugacity and temperature using the titanomagnetite-jimenite thermometry/oxygen barometry range from logfO(2) of -15.30 to -20.48 in host rocks, logfO(2) of -15.39 to -20.80 in the mafic microgranular enclaves and 617 +/- 6 to 758 +/- 23 degrees C in host rocks, 622 +/- 6 to 735 +/- 24 degrees C in the mafic microgranular enclaves, possibly indicating crystallisation temperature. Applying magnetite-ilmenite thermometry/oxygen barometry to the granitoid rocks also involves microprobe analyses of ilmenite lamellae in titanomagnetite and this method yielded mean temperatures of 679 +/- 18 degrees C. The specific forms and chemical properties of Fe-Ti oxides, and similarities in crystallization temperature and oxygen fugacity of the host rocks and the mafic microgranular enclaves (MME) obtained from the Fe-Ti oxide pairs imply that thermal equilibrium probably occurred between two contrasted magmas, which mixed in various proportions so that possibly a felsic and a more mafic magma interaction occurred in a convectively dynamic magma chamber during crystallization of the plutons. Probably, underplating may be responsible for genesis of the hybrid plutons. Thus, for mixing of coeval magmas derived from a lithospheric upper mantle (mafic end-member) and lower crust (felsic end-member), a thermal anomaly should be supplied. Upwelling of hot asthenospheric material results in thermal perturbation and melting of lithospheric mantle. Intrusion of hot lithospheric mantle-derived mafic rnagma then induced lower crustal melting, producing felsic melt. Mixing of the lower crust-derived melt and lithospheric mantle-derived magma formed the hybrid plutons. This process requires a post-collisional extensional tectonic setting during the Eocene in the Eastern Pontides.Öğe MINERALOGY AND GEOCHEMISTRY OF THE KIZILTEPE (CAMARDI-NIGDE) MN PROSPECT IN CENTRAL ANATOLIA, TURKEY(STEF92 TECHNOLOGY LTD, 2016) Lermi, Abdurrahman; Sonmez, Mustafa; Aydin, FarukThis paper is to investigate ore-alteration mineralogy and geochemical changes of wall rocks in Kiziltepe Mn mineralization (Camardi, SE-Nigde), which is located in Ulukisla Basin from the central part of the Turkey. Kiziltepe prospect, a fault controlled hydrothermal-type Mn mineralization, is hosted predominantly by Late Cretaceous to Early Tertiary volcanic and volcanoclastic rock series, which are submarine in character with trachytic to rhyolitic composition. After all samples were systematically collected from surface outcrops and the mineralized zones, they were investigated by petrographical and geochemical analysis. The results obtained from the microscopic and XRD analysis showed that the mineralization contained oxi-hydroxide Mn minerals such as manganite, pyrolusite, psilomelane, and manganese phosphate. Quartz, carbonates, sericite, clay minerals and barite are the gangue minerals. Quartz is ubiquitous and occurs both in the ore zone and in the wall rocks. Alteration mineralogy usually was formed fault-related to alteration zones. Alterations were characterized by presence of quartz and sericite, and locally extensively overprinted by kaolinite. Mass change calculations revealed that Al, Ti, and Y behaved as the least mobile elements during alteration and that footwall felsic rocks gained Fe, Si, K, Ca and ore forming constituents, respectively. The most characteristic chemical changes near the ore bodies were the Na depletion, mainly due to plagioclase destruction by the hydrothermal fluids. The BEE contents varied considerably depending on mass change effects related to alteration. An average grade of Mn in the fault zone has been reached about 22.47 %.Öğe Petrogenesis of the Neogene alkaline volcanics with implications for post-collisional lithospheric thinning of the Eastern Pontides, NE Turkey(ELSEVIER SCIENCE BV, 2008) Aydin, Faruk; Karsli, Orhan; Chen, BinWhole-rock geochemistry, Sr-Nd-Pb isotopes and K-Ar data are reported for alkaline samples collected from the Neogene alkaline volcanics (NAVs) in the Eastern Pontides, northeastern Turkey, in order to investigate their source and petrogenesis and geodynamic evaluation of the region. The NAVs were made of three groups that comprise of basanite-tephrite (feldspar-free; Group A), tephrite-tephriphonolite (feldspar and feldspathoid-bearing; Group B) and alkaline basalt-rhyolite (feldspathoid-free, Group C) series. These rocks cover a broad compositional range from silica-undersaturated to silica-oversaturated types, almost all of which are potassic in character. They show enrichment of LREE and LILE and depletion of HFSE, without a Eu anomaly in most of the mafic, samples. Textural features and calculated pressures based on the Cpx-barometer in each series indicate that the alkaline magma equilibrated at shallow crustal depths under a pressure of about 3-4.5 kbar and approximating a crystallization depth of 9-14 km. The NAVs are slightly depleted in isotopic composition, with respect to Sr-87/Sr-86 (ranging from 0.705018 to 0.705643) and Nd-143/Nd-144 (ranging from 0.512662 to 0.512714) that indicate young Nd model ages (0.51-059 Ga). This may indicate that the parent melts tapped a homogeneous and young lithospheric mantle source which was metasomatized by subduction-derived sediments during the Late Mesozoic. Pb isotopic compositions (Pb-206/Pb-204=18.85-18.95; Pb-207/Pb-204=15.60-15.74; Pb-208/Pb-204=38.82-39.25) may also be consistent with a model for an enriched subcontinental lithospheric mantle source. Lithospheric thinning and resultant upwelling of asthenosphere induced by lithospheric delamination may have favoured partial melting of chemically enriched, Young lithospheric mantle beneath the Eastern Pontides. Then, the melt subsequently underwent a fractional crystallization process along with or without minor amounts of crustal assimilation, generating a wide variety of rock types in a post-collision extensional regime in the Eastern Pontides during the Neogene. (C) 2008 Elsevier B.V. All rights reserved.Öğe Quaternary bimodal volcanism in the Nigde Volcanic Complex (Cappadocia, central Anatolia, Turkey): age, petrogenesis and geodynamic implications(SPRINGER, 2014) Aydin, Faruk; Schmitt, Axel K.; Siebel, Wolfgang; Sonmez, Mustafa; Ersoy, Yalcin; Lermi, Abdurrahman; Duncan, RobertThe late Neogene to Quaternary Cappadocian Volcanic Province (CVP) in central Anatolia is one of the most impressive volcanic fields of Turkey because of its extent and spectacular erosionally sculptured landscape. The late Neogene evolution of the CVP started with the eruption of extensive andesitic-dacitic lavas and ignimbrites with minor basaltic lavas. This stage was followed by Quaternary bimodal volcanism. Here, we present geochemical, isotopic (Sr-Nd-Pb and delta O-18 isotopes) and geochronological (U-Pb zircon and Ar-Ar amphibole and whole-rock ages) data for bimodal volcanic rocks of the Ni g de Volcanic Complex (NVC) in the western part of the CVP to determine mantle melting dynamics and magmatic processes within the overlying continental crust during the Quaternary. Geochronological data suggest that the bimodal volcanic activity in the study area occurred between ca. 1.1 and ca. 0.2 Ma (Pleistocene) and comprises (1) mafic lavas consisting of basalts, trachybasalts, basaltic andesites and scoria lapilli fallout deposits with mainly basaltic composition, (2) felsic lavas consisting of mostly rhyolites and pumice lapilli fall-out and surge deposits with dacitic to rhyolitic composition. The most mafic sample is basalt from a monogenetic cone, which is characterized by Sr-87/Sr-86 = 0.7038, Nd-143/Nd-144 = 0.5128, Pb-206/Pb-204 = 18.80, Pb-207/Pb-204 = 15.60 and Pb-208/Pb-204 = 38.68, suggesting a moderately depleted signature of the mantle source. Felsic volcanic rocks define a narrow range of Nd-143/Nd-144 isotope ratios (0.5126-0.5128) and are homogeneous in Pb isotope composition (Pb-206/Pb-204 = 18.84-18.87, Pb-207/Pb-204 = 15.64-15.67 and Pb-208/Pb-204 = 38.93-38.99). Sr-87/Sr-86 isotopic compositions of mafic (0.7038-0.7053) and felsic (0.7040-0.7052) samples are similar, reflecting a common mantle source. The felsic rocks have relatively low zircon delta O-18 values (5.6 +/- 0.6 %) overlapping mantle values (5.3 +/- 0.3 %), consistent with an origin by fractional crystallization from a mafic melt with very minor continental crustal contamination. The geochronological and geochemical data suggest that mafic and felsic volcanic rocks of the NVC are genetically closely related to each other. Mafic rocks show a positive trend between Sr-87/Sr-86 and Th, suggesting simultaneous assimilation and fractional crystallization, whereas the felsic rocks are characterized by a flat or slightly negative variation. High Sr-87/Sr-86 gneisses are a potential crustal contaminant of the mafic magmas, but the comparatively low and invariant Sr-87/Sr-86 in the felsic volcanics suggests that these evolved dominantly by fractional crystallization. Mantle-derived basaltic melts, which experienced low degree of crustal assimilation, are proposed to be the parent melt of the felsic volcanics. Geochronological and geochemical results combined with regional geological and geophysical data suggest that bimodal volcanism of the NVC and the CVP, in general, developed in a post-collisional extensional tectonic regime that is caused by ascending asthenosphere, which played a key role during magma genesis.Öğe Relative contributions of crust and mantle to generation of Campanian high-K calc-alkaline I-type granitoids in a subduction setting, with special reference to the Harsit Pluton, Eastern Turkey(SPRINGER, 2010) Karsli, Orhan; Dokuz, Abdurrahman; Uysal, Ibrahim; Aydin, Faruk; Chen, Bin; Kandemir, Raif; Wijbrans, JanWe present elemental and Sr-Nd-Pb isotopic data for the magmatic suite (similar to 79 Ma) of the Harsit pluton, from the Eastern Pontides (NE Turkey), with the aim of determining its magma source and geodynamic evolution. The pluton comprises granite, granodiorite, tonalite and minor diorite (SiO(2) = 59.43-76.95 wt%), with only minor gabbroic diorite mafic microgranular enclaves in composition (SiO(2) = 54.95-56.32 wt%), and exhibits low Mg# (<46). All samples show a high-K calc-alkaline differentiation trend and I-type features. The chondrite-normalized REE patterns are fractionated [(La/Yb)(n) = 2.40-12.44] and display weak Eu anomalies (Eu/Eu* = 0.30-0.76). The rocks are characterized by enrichment of LILE and depletion of HFSE. The Harsit host rocks have weak concave-upward REE patterns, suggesting that amphibole and garnet played a significant role in their generation during magma segregation. The host rocks and their enclaves are isotopically indistinguishable. Sr-Nd isotopic data for all of the samples display I(Sr) = 0.70676-0.70708, epsilon(Nd)(79 Ma) = -4.4 to -3.3, with T(DM) = 1.09-1.36 Ga. The lead isotopic ratios are ((206)Pb/(204)pb) = 18.79-18.87, ((207)Pb/(204)Pb) = 15.59-15.61 and ((208)Pb/(204)Pb) = 38.71-38.83. These geochemical data rule out pure crustal-derived magma genesis in a post-collision extensional stage and suggest mixed-origin magma generation in a subduction setting. The melting that generated these high-K granitoidic rocks may have resulted from the upper Cretaceous subduction of the Izmir-Ankara-Erzincan oceanic slab beneath the Eurasian block in the region. The back-arc extensional events would have caused melting of the enriched subcontinental lithospheric mantle and formed mafic magma. The underplating of the lower crust by mafic magmas would have played a significant role in the generation of high-K magma. Thus, a thermal anomaly induced by underplated basic magma into a hot crust would have caused partial melting in the lower part of the crust. In this scenario, the lithospheric mantle-derived basaltic melt first mixed with granitic magma of crustal origin at depth. Then, the melts, which subsequently underwent a fractional crystallization and crustal assimilation processes, could ascend to shallower crustal levels to generate a variety of rock types ranging from diorite to granite. Sr-Nd isotope modeling shows that the generation of these magmas involved similar to 65-75% of the lower crustal-derived melt and similar to 25-35% of subcontinental lithospheric mantle. Further, geochemical data and the Ar-Ar plateau age on hornblende, combined with regional studies, imply that the Harsit pluton formed in a subduction setting and that the back-arc extensional period started by least similar to 79 Ma in the Eastern Pontides.Öğe Slab break-off-related magnesian andesites and dacites with adakitic affinity from the early Quaternary Keciboyduran stratovolcano, Cappadocia province, central Turkey: evidence for slab/sediment melt-mantle interaction and magma mixing(Springer, 2022) Aydin, Faruk; Sonmez, Mustafa; Siebel, Wolfgang; Karsli, Orhan; Lermi, AbdurrahmanVoluminous moderate- to high-magnesian [Mg# = molar Mg/(Mg- + Fe2+) = 44-64] andesitic and dacitic rocks with high silica (mostly 61-66 wt%) adakitic affinity (Y = 13-22, Yb = 1.3-2.1, Sr/Y = 18-44, La/Yb = 10-25) and common mafic magmatic enclaves (MMEs) are first reported in the Keciboyduran stratovolcano (KSV) from the Cappadocia volcanic province (CVP), Central Anatolia, Turkey. We present comprehensive whole-rock geochemistry and Sr-Nd-Pb isotope data, mineral chemical compositions and 40Ar-39Ar ages for KSV samples. Based on the volcanostratigraphy and 40Ar-39Ar dating results, two successive eruption ages of 2.2-1.6 Ma (stage I: amphibole-rich) and 1.6-1.2 Ma (stage II: pyroxene-rich) were established for the KSV, corresponding to the Gelasian and Calabrian stages of Early Pleistocene, respectively. Textural and geochemical evidence indicates that the KSV magnesian andesites-dacites are products of a hybrid magma formed by mixing between mantle-derived mafic and crust-derived felsic magmas with further fractionation and minor contamination during magma storage and ascent. Our new data, combined with previous geological and geophysical results suggest that parental magnesian mafic melts of the KSV rocks originated from a heterogenous mantle source generated through the metasomatism of mantle wedge material by subducted sediment-derived melts, and then partially melted through asthenospheric upwelling in response to slab break-off. The mafic magma underplated the overlying lower crust, resulting in its partial melting to generate crustal felsic magma. Both magmas mixed at lower crustal levels creating MME-rich hybrid magmas. Subsequently, the hybrid magmas were emplaced at different depths of the crust (c. 4-11 and 11-15 km for the stage I and II, respectively), where they crystallized at moderate temperatures (c. 1180-840 degrees C) and under relatively high oxygen fugacity (LogfO(2) = - 11.4 to - 9.2), water-rich (H2Omelt = 5.6-3.6 wt%) and polybaric (similar to 1.2 to 5.1 kbars) conditions, and underwent fractionation of primarily amphibole +/- pyroxene causing adakitic affinity. We propose a new petrogenetic model for the early Quaternary magnesian/adakitic andesites/dacites of the CVP in a post-subduction tectonic setting. Our results provide robust evidence for slab break-off of the eastern Cyprus oceanic lithosphere and put further constraints on the tectonic evolution of the eastern Mediterranean collision zone during the Early Quaternary.
