Gümüşhane ÜniversitesiGümüşhane ÜniversitesiAçık Erişim Arşivi · RDL Open

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  • MakaleYalnız künye2004
    Magma interaction recorded in plagioclase zoning in granitoid systems, Zigana Granitoid, eastern Pontides, Turkey

    Karsli, Orhan; Aydin, Faruk; Sadiklar, M. Burhan

    Plagioclase crystals characterized by compositional zoning are typical of the Zigana Granitoid (ZG), NE Turkey. The zoned crystals, which show textural equilibrium with the assemblage quartz + plagioclase + K-feldspar + hornblende + biotite + pyroxene, + magnetite + ilmenite, exhibit oscillatory zoning. The zoned plagioclase crystals, ranging in size from 3 to 6 mm, are oval and larger than normal lath-shaped crystals. The zoned crystals are divided petrographically into two main types: (i) crystals zones only at their rims, with spongy cores; and (ii) completely zoned ones. Composition of the zoned crystals ranges from An23 (oligoclase) to An70 (labradorite). Plagioclase crystals with oscillatory zoning are governed by strong substitution mechanisms of Ca2+ ⌊ Na+, Al 3+ ⌊ Sl4+ and weak substitution of Fe3+ for Sl4+. The Fe2O3 (t) (wt %) contents of the subject plagioclases increase with increasing An content. The petrographic and compositional changes from rim to rim (oscillatory zoning), and positive correlation between Fe2O3(t) (wt %) and An (mol %) contents of the zoned plagioclases, suggest recurrent mafic magma injection into a felsic magma chamber, and thus magma interaction as a dominant magmatic process during the evolution of the Zigana Granitoid (ZG).

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  • MakaleYalnız künye2004
    The morphology and chemistry of K-feldspar megacrysts from Ikizdere Pluton: Evidence for acid and basic magma interactions in granitoid rocks, NE-Turkey

    Karsli, O.; Aydin, F.; Sadiklar, M.B.

    Ikizdere Pluton consists of granite, granodiorite, tonalite, monzonite, quartz monzonite containing pinkish colored K-feldspar megacrysts (KFMs). The crystal sizes of the KFMs range from 1 to 4 cm. The lath-shaped megacrysts are uniformly (i.e., randomly) distributed in the host plutonic rocks and have mafic and felsic inclusions whose crystal sizes are smaller than 1 mm. The crystal inclusions are biotite, slightly annitic in composition with XMg[=Fetot/(Fetot+Mg)]=0.50-0.58, amphibole (magnesio-hornblende, XMg[=Mg/(Mg+Fetot) ]=0.70-0.79), iron-titanium oxide (low titanium magnetit and ilmenite), plagioclase (Ab75-25An65-35) and as minor quartz. The compositions of the KFMs range from Or95Ab5An0 to Or82Ab17An1. BaO contents of the megacrysts increase from core to rim. The mafic and felsic inclusions are compositionally similar those of the host rocks. The chemical and textural features of K-feldspar are typical for megacrysts that grew as phenocrysts in dynamic granitoidic magma systems. The overgrowth of KFMs and mafic magma injections (magma mixing) may be related to temperature, pressure and compositional fluctuations in the magma chamber. Remnant of earlier formed K-feldspar crystals remain in the felsic magma system, while the mafic injection can decompose some earlier precipitated KFMs. The remnant of K-feldspar remaining after mafic injection are overgrown by rapid diffusion of Ba, K and Na elements in liquid phase, during the later stages of crystallization of the host magma.

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  • MakaleYalnız künye2003
    Mineralogy and chemistry of biotites from Eastern Pontide granitoid rocks, NE-Turkey: Some petrological implications for granitoid magmas

    Aydin, F.; Karsli, O.; Sadiklar, M.B.

    The Eocene Zigana Granitoid in the northern zone and the Middle-Upper Eocene Dolek and Saricicek Plutons in the southern zone of the Eastern Pontides (NE-Turkey) consist of different rock series ranging in composition from intermediate to felsic compositions containing from <1% to 9% of biotite. The biotites are Mg-rich (XFe = Fe2+/Fe2+ + Mg) = 0.28 - 0.49) in the southern zone plutons and Mg- to Fe-rich (XFe = Fe2+/Fe2+ + Mg) = 0.33 - 0.78) in the northern zone pluton. They coexist with K-feldspar, plagioclase, quartz, amphibole, pyroxene, low titanium magnetite, minor ilmenite titanite. Biotites have been buffered by the Ni-NiO. The plutons equilibrated under low oxygen fugacities (LogfO2) ranging from -16.01 to -20.23 bars for Dolek and Saricicek, and -16.70 to -17.90 bars for Zigana. EPMA indicate that the composition of biotite is related to the mineral assemblages of Dolek, Saricicek and Zigana biotites as a consequence of chemistry of the magma and the physical conditions during crystallization. The biotite compositions were used to discriminate the tectonic setting of the plutons. The intrusions appear to be related to calc-alkaline to high-K calc-alkaline orogenic suites. Furthermore, Mg(6)-Fetot substitution has played a significant role during the crystallization of the biotites.

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