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- MakaleYalnız künye2008Scopus SJRQ1Elemental 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
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 40Ar/39Ar 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 87Sr/86Sr = 0.70404-0.70587 and slightly depleted Nd isotopic compositions (εNd from - 0.9 to 2.8), with significantly varied Mg# ranging from 2 to 53. Pb isotopic compositions [206Pb/204Pb = 18.90-19.02, 207Pb/204Pb = 15.64-15.70, 208Pb/204Pb = 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.
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İncele - MakaleYalnız künye2006Scopus SJRQ2Pre-eruptive conditions revealed by mega- and pheno-cryst compositions from the Quaternary Erzincan Volcanics, Eastern Turkey: Insights into the magma processes
Karsli, Orhan
Quaternary Erzincan Volcanics (QEVs) from the Erzincan Basin consist of mega- and pheno-cryst-bearing high-K calc-alkaline dome lavas. Fourteen nearly phenocrystic domes, with a range of basaltic-andesite, andesite, dacite and rhyolite compositions, were emplaced in the North Anatolian Fault Zone. The emplacement ages yielded by the unspiked K-Ar technique range from 102 to 140 ka. The andesitic domes (each less than 3 km in diameter) contain amphibole megacrysts. Amphibole compositions show a linear variation from ferro-edenite, edenite to pargasite from rhyolite to andesite. Pargasitic amphibole megacrysts scattered into the groundmass are very similar in composition to the microlites. All plagioclases are <An53 mol%. Oscillation types are An32-50 whose variations range from 10 to 16 mol% An and have 10-150 μm in thickness. Pre-eruptive conditions, calculated from mega- and pheno-cryst composition, using pyroxene and two oxide thermometers and the Al-in-hornblende barometer, ranged from 918 to 837 °C and 6.6 to 4.3 kbar for andesitic magma, 824-755 °C and 4.6-4.2 kbar for dacitic magma to 803-692 °C and 4.3-3.9 kbar for rhyolitic magma, which correspond to a depth of >10 km for storage region of the crust. The fO2 values vary from -14.25 to -15.35 log units which are plotted just below nickel-nickel oxide (NNO) buffers. The systematic decrease in thermobarometric results from andesite to rhyolite is consistent with a single magma reservoir moving upward through the crust followed by fractional crystallization. Textural and compositional relationships of mega- and pheno-crystic phases suggest that magma mixing, fluid input to the reservoir and fractional crystallization processes, with a small amount crustal contamination play key role in evolution of the QEVs.
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