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    Magma interaction recorded in plagioclase zoning in granitoid systems, Zigana Granitoid, Eastern Pontides, Turkey
    (SCIENTIFIC TECHNICAL RESEARCH COUNCIL TURKEY-TUBITAK, 2004) Karsli, O; Aydin, F; Sadiklar, MB
    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 An(23) (oligoclase) to An(70) (labradorite). Plagioclase crystals with oscillatory zoning are governed by strong substitution mechanisms of Ca2+ double left right arrow Na+, Al3+ double left right arrow Si4+ and weak substitution of Fe3+ for Si4+. 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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    Mineralogy and composition of the chromitites and their platinum-group minerals from Ortaca (Mugla-SW Turkey): evidence for ophiolitic chromitite genesis
    (SPRINGER WIEN, 2005) Uysal, I; Sadiklar, MB; Tarkian, M; Karsli, O; Aydin, F
    A large number of podiform chromitite bodies of massive, disseminated and nodular type have been located in ultramafic units, composed of depleted mantle harzburgite and dunite of the Marmaris Peridotite from Ortaca (Mugla, SW Turkey). The chromite ore bodies are surrounded by dunite envelopes of variable thickness, exhibiting transitional boundaries to harzburgite host rocks. Chromitites, containing a large number of inclusions, i.e. silicates, base metal sulphides and alloys, and platinum-group minerals (PGM) ;have a wide range of chemical composition. The Cr# [Cr/( Cr+Al)] values of most chromitites are high (0.61 - 0.81) and Mg# [Mg/(Mg+Fe2+)] values range between 0.65 and 0.71 with TiO2 content lower than 0.24wt.%, which may reflect the crystallization of chromites from boninitic magmas in supra-subduction setting environment. Platinum-group minerals ( PGM) such as laurite, erlichmanite and Os - Ir alloys, silicates such as olivine, clinopyroxene and amphibole, and base metal sulphides (BM-S), alloys (BM-A) and arsenides (BM-As) are found as inclusions in chromite or in the serpentine matrix. Platinum-group element (PGE) concentrations of the Ortaca chromitites (OC) are low in all samples. Total PGE ( Ir+Ru+Rh+Pt+Pd) ranges from 63 ng/g to 266ng/g and Pd/Ir ratios range between 0.23 and 4.75. PGE content is higher and the Pd/Ir ratio lower in Cr-rich chromitites compared to Al-rich ones. There is a strong negative correlation between the Cr# and Pd/Ir ratios ( r = - 0.930). The PGE patterns show a negative slope from Ru to Pt and a positive slope from Pt to Pd. The low PGE content in the majority of the OC may reflect a lack of sulphur saturation during an early stage of their crystallization. The laurite compositions show a wide range of Ru - Os substitution caused by relatively low temperature and increasing f(S-2) during the chromite crystallization. The high Cr# of and hydrous silicate mineral inclusions in chromite imply that chromite crystallized in a supra-subduction setting.