34 research outputs found
Compositional variations of chromite and solid inclusions in ophiolitic chromitites from the southeastern Turkey: Implications for chromitite genesis
Chromitites, associated with upper mantle peridotites of ophiolites from southeastern Turkey, are lenticular bodies or veinlets made up of massive, banded and disseminated chromite. Chromite shows a wide range of Cr# [Cr/(Cr+Al)] varying between 0.42 and 0.81, and Mg# [Mg/(Mg+Fe2+)] of 0.45 to 0.75. Geochemically, they are divided into two compositional groups, such as high-Cr (Cr#?0.7) and high-Al (Cr#<0.6). The contents of the platinum-group elements (PGE) in high-Cr chromitites range between 42 and 348ppb (average 158ppb), whereas high-Al ones are represented by a lower total PGE, ranging between 70 and 94ppb (average 84ppb). However, two high-Cr chromitite samples showed significant enrichments especially of Ir-subgroup of PGE (IPGE: Os, Ir, Ru) with total PGE contents reaching up to 2.7ppm. The chromitites mostly contain tiny inclusions (<5µm) of platinum-group minerals (PGM). The most abundant PGM is laurite which is rarely associated with irarsite±Os-Ir alloys; these minerals in particular are more abundant in high-Cr chromitites, especially in PGE enriched chromitites. The primary base-metal sulfide (BMS) inclusions consist of millerite and to a lesser extent pentlandite, and very rarely pyrite. Violarite, polydymite and heazlewoodite form the secondary BMS phases found mostly in altered silicate matrix. Both PGM and BMS are frequently associated with the silicates: amphibole, olivine and clinopyroxene. Textural relationships and the composition of PGM and BMS inclusions suggest that they crystallized at varying temperature (1300°C-1000°C) and sulfur fugacity conditions, before or during the event of crystallization of chromite. The high-Cr chromitites crystallized in equilibrium with boninite melt, probably originated in a supra-subduction zone (SSZ), while the high-Al chromitites crystallized in equilibrium with middle oceanic ridge basalt (MORB) type melts. The presence of amphiboles in high-Al chromitites suggests hydrous parental melts that could be produced, most probably, in back-arc tectonic setting. © 2013.109Y219This paper is a part of Recep Melih Akmaz's Master thesis, and financially supported by the TUBITAK project (#109Y219 ). We thank José Maria González-Jiménez for his review of an earlier version of this manuscript. We are very grateful to Karl Thomas Fehr and Rupert Hochleitner for giving us a chance to use the electron microprobe laboratory, and Dirk Müller and Melanie Kaliwoda for their great help during the electron-microprobe analyses. We are grateful for the help of Monica Escayola and Jody Spence during the trace element analyses of chromite by LA-ICP-MS. Also, many thanks are due to Yılmaz Demir for the sample preparation. Adem Eşki, Abdullah Dede and A. Haydar Aygün are gratefully thanked for their help during the field work. The authors are grateful to Franco Pirajno for editorial handling, and to Argyrios Kapsiotis and one anonymous referee for their constructive reviews, which greatly improved our manuscript
Investigation of the Molecular Structure of Turkish Asphaltenes
Molecular structure of asphaltenes prepared from four Turkish crude oils with different origin were characterized by elemental analysis, proton nuclear magnetic resonance (1H NMR), gel permeation chromatography (GPC) by X-ray diffraction (XRD) and by Fourier transform infrared spectroscopy (FTIR). The X-ray diffraction method was used to investigate the crystallite and aromaticity parameters of the asphaltenes. Average distance between the aromatic sheets, average distance between the aliphatic chains, average diameter of the cluster, and average number of aromatic sheets per stack parameters were calculated for the asphaltenes. The combined NMR, FTIR, molecular weight, elemental content, and XRD results have been used to calculate hypothetical structure of the Turkish asphaltenes
Ophiolitic chromitites from the Kızılyüksek area of the Pozantı-Karsantı ophiolite (Adana, southern Turkey): Implication for crystallization from a fractionated boninitic melt
Ophiolitic rocks are widely distributed in Turkey. One type, the Pozantı-Karsantı ophiolite from southern Turkey, contains a large number of chromitite deposits located mostly in the mantle peridotites and close to the Moho transition zone dunite and cumulate dunites. Cr-spinel grains from the chromitites are represented by high Cr# [100 × Cr / (Cr + Al) = 68–81], and their Mg# [100 × Mg / (Mg + Fe2 +)] range from 54 to 71. Gallium and Co contents vary between 18 and 32 ppm and 185–266 ppm, respectively, and they show negative correlation with Cr#. A detailed optical investigation reveals that the Cr-spinel grains contain silicate, platinum-group mineral (PGM) and base metal sulfide (BMS) inclusions. Single phase inclusions of amphibole are the only hydrous silicate phases in the investigated chromitites, and they contain low TiO2 (< 0.43 wt.%). Olivine, with high Fo (~ 96) and NiO contents (0.48–0.68 wt.%), and clinopyroxene, with low TiO2 (< 0.1 wt.%), Al2O3 (< 2.84 wt.%) and Na2O contents (< 0.4 wt.%) were also observed as primary silicate inclusions. Chromitites contain low concentrations of total platinum-group elements (PGE) ranging between 32 and 162 ppb, with an average value of 93 ppb. Primitive mantle-normalized PGE diagrams show almost flat to positive slopes from Os to Rh (RhN/OsN = 0.99 to 8.5) and negative slope from Rh to Pt and Pd. All samples show marked positive Ru anomalies. Consistent with the geochemical data, Ru, Os, and Ir bearing PGE sulfide (laurite-erlichmanite solid solution series [(Ru, Os)S2–(Os, Ru)S2] phases) are the most common PGM detected in the investigated chromitite samples. They show a narrow range of Os-Ru substitution [Ru#; Ru/(Ru + Os) = 0.72–0.97], indicating no erlichmanite in the PGM paragenesis. In addition to the most common PGM laurite, several osmium (Os, Ir), iridium (Ir, Os), irarsite, and one single grain of speryllite (PtAs2) were detected as magmatic inclusions in Cr-spinel. Three unknown PGE/PGE–BME (base metal element) phases were also detected in Cr-spinel grains with compositions that correspond to the chemical formulas of (Os, Ru, Ir, Rh, Fe, Pd)2S5, Ir(Rh,Pt,Ni,Cu)S3, and (Ir, Rh, Ru)2(Ni, Cu)S3, respectively. The high Cr# and low Ti content of Cr-spinel grains and amphibole inclusions with low Ti content as hydrous phases in Cr-spinel grains require a hydrous melt depleted in incompatible trace elements for the formation of investigated chromitites; therefore, we suggest a fore arc tectonic environment for the generation of Kızılyüksek chromitites. The presence of Os-Ir alloys and Ru-rich laurites implies that Cr-spinel crystallization took place at relatively high temperature (1100–1300 °C) and low ƒ(S2) (between - 1 and - 3) conditions. Major and trace element compositional variations of Cr-spinel, wide variation of RhN/OsN ratios of the chromitites and depletion of Os in the chromitites compared to Ir and Ru may imply that Kızılyüksek chromitites crystallized from a variously fractionated boninitic melt. © 2016 Elsevier B.V
The Structural Characterization of Saturate, Aromatic, Resin, and Asphaltene Fractions of Batiraman Crude Oil
The structural characterization of fractions of Batiraman crude oil, which is the heavy crude oil from a field in the southeastern part of Turkey, was investigated. Batiraman crude oil and its saturate, aromatic, resin, and asphaltene (SARA) fractions were seperated. Treatment of crude oil with n-heptane provided the separation of asphaltene. Maltene was collected by evaporating the n-heptane from the filtrate. Then, maltene was separeted into saturates, aromatics, and resins by SARA technique. Maltene was separated into saturate, aromatic, and resin fractions using column chromatography. SARA fractions were quantified on a weight percent basis. Fractions of Batiraman crude oil were characterized by elemental analysis, proton nuclear magnetic resonance (1H NMR) analysis, electrospray ionization mass spectrometry (ESI-MS), and Fourier transform infrared (FTIR) spectroscopy techniques
Coexistence of compositionally heterogeneous chromitites in the Antalya-Isparta ophiolitic suite, SW Turkey: A record of sequential magmatic processes in the sub-arc lithospheric mantle
The Antalya-Isparta region in southwestern Turkey is well known for its large ophiolitic peridotite exposures, which host various chromite orebodies. These are small-sized, massive to disseminated in texture chromitites occurring in the form of lenses or veinlets, and commonly surrounded by dunite envelopes of variable thickness. Chromitite seams from the Antalya mantle suite are both high- and intermediate-Cr varieties (Cr# = 0.56-0.83), whereas chromitites in the Isparta mantle sequence are exclusively Cr-rich (Cr# = 0.75-0.85). In situ minor and trace element abundances obtained by LA-ICP-MS analyses of unaltered Cr-spinel from the Cr-rich chromitites are comparable to those reported in Cr-spinel of chromitites from typical fore-arc peridotite complexes. However, minor and trace element concentrations in Cr-spinel from intermediate chromitites are dissimilar to those acquired from Cr-spinels of chromitites from well-known back-arc basin-derived ultramafic massifs. Calculation of parental magma compositions indicates that both types of chromitites share a common parentage with progressively fractionating arc-related melts. The studied chromitites are characterized by a systematic enrichment in IPGE [Os, Ir, and Ru (41-317 ppb)] with respect to PPGE [Rh, Pt, and Pd (3-49 ppb)], resulting in negatively-sloping chondrite-normalized PGE patterns that are less fractionated in intermediate chromitites. Their noble mineral assemblage is vastly dominated by tiny (?10 µm) euhedral laurite crystals, followed by subsidiary irarsite and trivial amounts of Os-Ir alloy grains. PGM grains are not encountered in the intermediate chromitites, potentially due to crystallization resulting from PGE-poor melt. Laurite is Os-poor and exhibits a narrow range of Os-for-Ru substitution [Ru/(Ru + Os) = 0.75-0.99]. However, the concomitance of laurite and millerite in the Cr-rich chromitites of the mutual Antalya-Isparta mantle suite is in favour of their precipitation from an Os-depleted melt, characterized by local and rapid variations of fS2 prior to or coevally with Cr-spinel crystallization. Moreover, the presence of amphibole inclusions in Cr-spinel indicates that the melt-triggered chromitite genesis potentially involved a hydrous component. Overall, data suggest that investigated orebodies were produced by a successively fractionating arc-derived melt that generated compositionally distinct chromitites at two different pseudo-stratigraphic levels within the Antalya-Isparta arc-type mantle suite. © 2016 Elsevier B.V.109Y219This study was supported by scientific project funded by TUBITAK ( #109Y219 ). Dirk Müller, Rupert Hochleitner and Melanie Kaliwoda are acknowledged for their generous help with the electron microprobe analyses. We thank Utku Bağcı and Tamer Rızaoğlu for their help during the field work. Fernando Gervilla, Joaquin Proenza and José María González-Jiménez are also greatly thanked for their help with the SEM images and additional electron microprobe analyses of platinum-group minerals. We thank the editor Andrew Kerr and two anonymous reviewers for their constructive comments, which helped us to improve the manuscript
The Guleman ophiolitic chromitites (SE Turkey) and their link to a compositionally evolving mantle source during subduction initiation
Economically viable chrome ore bodies are hosted within a unit of pervasively serpentinized harzburgite in the Guleman mine of the homonymous ophiolite in SE Turkey. Chrome ores consist of m- to tens of m-scale tectonically imprinted chromitite bodies, showing semi-massive to massive texture and podiform to lenticular morphology. They are hosted in dunite envelopes of variable thickness and are composed of chromian spinel [Cr-spinel] with high Cr# [Cr/(Cr + Al) = 0.61–0.81] and Mg# [(Mg/Mg + Fe2+) = 0.56–0.72], and low TiO2 (0.06–0.33 wt%) content. Compositionally, they are divided into intermediate-Cr (CrSp#: 0.61–0.69) and high-Cr chromitites (Cr#Sp: 0.71–0.81). Chromian spinel from the intermediate-Cr chromitites is richer in Ni, Ti, Zn and Ga compared to that from the high-Cr chromitites. Both chromitite types show a general enrichment in IPGE (Os, Ir and Ru) over PPGE (Rh, Pt and Pd). The PGM assemblages of these chromitites are dominated by small (?6 µm), idiomorphic inclusions of Ru-Os bisulfides and subordinate Os-Ir-Ru alloy in Cr-spinel. Bisulfides within the intermediate-Cr chromitites show a wider range of Os-for-Ru substitution than those hosted in the Cr-rich chromitites [Ru/(Ru + Os): 0.15–0.86 vs. 0.71–0.86, respectively]. Geochemical calculations and PGE-mineralogical data demonstrate that the parental melts of the investigated chromitites had variable Al2O3 (10.62–14.58 wt%) and S contents. This implies a range of magma compositions generated at different degrees of partial melting of a common depleted mantle source. The calculated range of compositions is not consistent with a typical mid-ocean ridge or mature suprasubduction zone setting, but is thought to be representative of the evolving composition of a deep-seated, heterogeneous mantle source during subduction initiation beneath a forearc basin. © 2017 Elsevier B.V.109Y219 National Council for Scientific Research National Natural Science Foundation of China: NNSFC National Social Science Fund Youth Project: 41402065Financial support for this work was made available by The Scientific and Technological Research Council of Turkey ( TÜBİTAK ) with grant # 109Y219 . Part of this research was also supported by a Youth Science Fund Project (No. 41402065 ) awarded from the National Natural Science Foundation of China (NNSFC) to A. Kapsiotis. Dirk Müller, Rupert Hochleitner and Melanie Kaliwoda are acknowledged for their generous help with the electron microprobe analyses. We thank Utku Bağcı and Tamer Rızaoğlu for their help during the field work. We would also like to express our gratitude to F. Pirajno, Editor-in-Chief of Ore Geology Reviews and two anonymous reviewers for their constructive feedback and insightful comments, which greatly improved an earlier version of our manuscript