Yazar "Sadiklar, M. Burhan" seçeneğine göre listele

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    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. Burhan
    Clinopyroxene 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.
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    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. Burhan
    Magnetite-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.