Musa Alpaslan

Geochemical and Pb-Sr-Nd Isotopic Constraints Indicating an Enriched-Mantle Source for Late Cretaceous to Early Tertiary Volcanism, Central Anatolia, Turkey

Bulk-rock major, trace, and REE geochemistry and Pb-Sr-Nd isotopic compositions identify mantle sources involved in the genesis of volcanic rocks of the Upper Cretaceous-Lower Tertiary Ulukişla Formation, Çamard-Ulukişla Basin, Nigde Province, central Anatolia. Incompatible trace-element patterns exhibit a large Nb-Ta trough and strong enrichment of LILE such as Ba, Th and U, and LREE, which indicate a subduction-zone signature. Trace-element ratios are compatible with a subcontinental lithospheric source. Isotopic data demonstrate the presence of an EMII-like protolith (87Sr/86Sr = 0.707242-0.707582, 143Nd/144Nd = 0.512336-0.512390, 206Pb/204Pb = 18.70-18.917, 207Pb/204Pb = 15.716-15.796, 208Pb/204Pb = 39.157-39.45). These geochemical and isotopic data indicate the derivation of the studied volcanic rocks from an enriched subcontinental mantle source, modified by earlier subduction events. This petrogenetic conclusion is compatible with a geodynamic setting of post-collisional extension for the Çamard-Ulukişla Basin.

Interactions Between Uronic Acids and Chromium(III)

Laboratory ion-exchange experiments were performed to investigate the complexation behavior of Cr(III) with uronic acids, such as galacturonic, glucuronic, and alginic acid (main constituents of bacterial exopolymeric substances). The experimental data were analyzed with a chemical equilibrium model in FITEQL to determine the reaction stoichiometries and stability constants for the formation of Cr-ligand complexes. Analysis of ion-exchange data with a chemical model indicates that the accurate description of Cr(III) complexation with both glucuronic and galacturonic acids requires postulation of a mixture of 1:1/1:2 complexes between Cr(III) and ligands under the experimental conditions studied (e.g., pH 4), but that the Cr-alginic acid binding can be modeled based on a reaction stoichiometry of 1:1 Cr-alginic acid complexes. Because of the complex nature of alginic acid, a nonelectrostatic, discrete ligand approach was used to determine proton and Cr binding with the functional groups of alginic acid. In this approach, alginic acid was conceptualized as being composed of a suite of two monoprotic acids (HL1 and HL2) with arbitrarily assigned pKa values of two and four, respectively. The results indicate that Cr binding with uronic acids mainly occurs through carboxylic groups under acidic to slightly alkaline pH conditions (e.g., pH < 8). The overall results of the present study indicate that the formation of such Cr-ligand complexes may have a pronounced effect on Cr(III) transport, solubility and bioavailability in natural systems.

Two-Stage Felsic Volcanism in the Western Part of the Southeastern Anatolian Orogen: Petrologic and Geodynamic Implications

We describe the petrogenesis of three phases of Late Oligocene to Middle Miocene felsic volcanism that occurred in the western part of the southeastern Anatolian orogen. All units are calcalkaline. The S-type character of these volcanic rocks is supported by their peraluminous natures (A/CNK 1.11-3.14) and high (up to 9.89%) normative corundum contents. Elevated Rb/Sr ratios and low MgO and Fe2O3total of the first phase suggest that it might represent melts lacking entrained Fe-Mg-rich crystals, and that the magma developed by muscovite-dehydration melting. Relatively lower Rb/Sr ratios and higher Ba, Sr and Eu concentrations, and high zircon-saturation temperatures of the last two phases, indicate that these melts formed by water-saturated melting. The felsic volcanism of Southeast Anatolia was initiated during continental collision as a result of convergence between the Eurasian and Arabian plates, and occurred during both collisional and post-collisional periods. During the former, volcanism (the first phase) occurred by anatexis of the muscovite-bearing Pütürge metamorphic rocks as a result of imbricate crustal thickening during the Late Oligocene-Early Miocene. In the Middle Miocene, continental exhumation and lithospheric fracturing caused partial fusion of the mantle beneath the Anatolian crust. Emplacement of hot, mantle-derived mafic melts in Anatolian lower crustal levels caused heating that led to partial melting, yielding felsic magmas of the second stage of volcanism (the last two phases).

Early to Middle Miocene intra-continental basaltic volcanism in the northern part of the Arabian plate, SE Anatolia, Turkey: geochemistry and petrogenesis

Continental basalts ranging in age from 16.5 to 19.08 Ma crop out throughout the northern part of the Arabian plate. The basalts have distinctive petrographic characteristics such as rounded and skeletal olivine phenocrysts with abundant melt inclusions, implying the mixing of two distinct magmas. All of the analysed basalts are tholeiitic in composition. The presence of quartz xenocrysts with clinopyroxene rims in some samples indicates that crustal assimilation was probably an important process during magma ascent to the surface, and low Mg number and high SiO 2 contents of the basalts clearly show that they have experienced fractional crystallization as well as crustal contamination. Variations of the major and trace elements versus MgO show that olivine + clinopyroxene + plagioclase were the main fractionating minerals. In terms of incompatible trace elements, the basalts have OIB-like signatures with a slight depletion at Nb–Ta on primitive-mantle-normalized diagrams. The basalts have slightly LREE enriched patterns with La/Yb N = 5.5 to 6.7. La/Nb ratios are close to unity, suggesting the melts may have originated in the asthenospheric mantle. Partial melting modelling based on REE data imply that the melts were not produced from a single mantle source depth, which is either purely a spinel- or garnet-peridotite end member. The samples lie on a binary mixing line between low-degree melts ( 10 %) from spinel-peridotite sources on a plot of La/Yb v. Dy/Yb, requiring interaction of melts derived from both garnet- and spinel-peridotite fields. Melts originating from both sources were initially tapped by distinct magma chambers, which subsequently hybridized into a single flow. Hybridized magma ascended to the surface along Neogene strike-slip faults, which are linked to the Dead Sea Fault Zone.

Petrographic and Geochemical Evidence for Magma Mixing and Crustal Contamination in the Post-Collisional Calc-Alkaline Yozgat Volcanics, Central Anatolia, Turkey

Petrographic, major-oxide, and trace-element data are presented for the Yozgat volcanics. These rocks range in composition from basalts through basaltic andesites and andesites to dacites. Major-oxide variations are largely explicable in terms of fractional crystallization, involving removal of observed phenocrysts and microphenocrysts. However, complex zoning patterns and resorbtion phenomena shown by phenocrysts in these lavas, and observed epitaxitic pyroxene growth around quartz xenocrysts imply that they are hybrids formed by a mixing process. In addition, observed enrichments in crustal elements such as K, Rb, Ba, Sr, and P provide clear evidence for the crustal assimilation of granitoid and metasedimentary xenoliths. The following model is suggested for the evolution of the Yozgat volcanics. The primitive magma underwent fractionation in an intracrustal magma chamber to yield more evolved liquids. Influx of hot, primitive magma into the magma chamber promoted vigorous convection-crustal assimilation and eruption of the volcanic rocks in the study area.

Quaternary basaltic volcanism reflecting heterogeneous mixture of two mafic melts: Gölova basaltic rocks, Southern Anatolia, Turkey

The Quaternary volcanic rocks from Gögova region constitute an example of on intra-continental volcanism in Southern Anatolia, Turkey. These rocks were erupted along the left-lateral strike-slip Yumurtalιk fault zone. They comprise basaltic lavas containing mafic enclaves. The enclaves are distributed widely through the lavas and are spherical to ellipsoidal in shape. Both the host lavas and the mafic enclaves have an alkaline character. Fractional crystallization process was important in the formation of the mafic enclaves where olivine was the main crystallizing phase. However, fractional crystallization was not a dominant process in the host lavas. Geochemical and petrological characteristics of both the mafic enclaves and the host lavas imply that magma mingling occurred during or immediately before eruption.