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    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, Raif
    Whole-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.
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    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, Cueneyt
    The 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.
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    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, Bin
    Whole-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.
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    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, Jan
    We 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.