Modjarrad, Monir; Uysal, Ibrahim; Yara, Irfan O. M. A.; Sen, Ahmet Dundar; Xin, Guangyao; Müller, Dirk

We present an integrated petrological, mineral-chemical, whole-rock geochemical, microstructural, and phase-equilibrium study of the West Maku metamafics (WMM), an ophiolite-related mafic unit in NW Iran. The WMM comprises garnet amphibolites and amphibole-bearing high-grade metamafic rocks containing almandine-rich garnet, tschermakite-ferro-tschermakite, andesine, epidote/zoisite, annite, muscovite-phengite, spinel, ilmenite, chlorite, quartz, and K-feldspar. Immobile element systematics indicate a tholeiitic, MORB-like basaltic protolith; LILE and crust-sensitive element enrichment likely reflect inherited crustal/sediment-derived components and metamorphic redistribution during subduction-accretion and/or m & eacute;lange assembly. P-T modelling defines four relative stages: M1, upper greenschist-facies metamorphism at ca. 6.4 kbar and 360 degrees C; M2, prograde heating to 8.0-8.4 kbar and 700-720 degrees C; M3, peak upper-amphibolite- to granulite-facies conditions at 9.0-9.8 kbar and up to 810 degrees C, with localized anatexis; and M4, retrogression at ca. 3.8 kbar and 520 degrees C. The clockwise path records the burial and heating of MORB-derived crust in a subduction-accretionary setting, followed by collision-related thermal relaxation/crustal thickening and subsequent uplift. Regional comparisons indicate thermally heterogeneous evolution along the central Neo-Tethyan suture across Armenia, SE T & uuml;rkiye, NE Iraq and NW Iran.

Akmaz, Recep Melih; Uysal, Ibrahim; Su, Ben-Xun; Sen, Ahmet D.; Hu, Wen-Jun; Seitz, Hans-Michael; Mueller, Dirk; Eslami, Alireza

This study presents a complete alteration sequence in chromitites from the Kizildag ophiolite (southern T & uuml;rkiye), documenting three distinct chromite types that record processes related to Neotethyan subduction. Chromitites exhibit predominantly lenticular forms and occasionally banded textures, embedded within mantle peridotites and the mantle-crust transition zone, specifically harzburgite and dunite. Our analysis categorizes chromite grains into three groups: fresh, altered, and porous. Fresh chromites are characterized by high contents of Cr2O3 ranging from 42.69 to 57.08 wt% and Al2O3 from 12.46 to 25.34 wt%. In contrast, altered chromites, typically located along fractures or at the edges of fresh grains, show significant variability in chemical composition, with Cr2O3 content between 43.34 and 63.94 wt% and Al2O3 between 2.91 and 14.84 wt%. Porous chromites, distinguished by their porous structure, present Cr2O3 contents from 44.58 to 52.66 wt% and Al2O3 from 3.00 to 8.38 wt%. Notably, altered and porous chromites demonstrate substantial enrichments in Fe and trace elements such as Mn, Ni, Zn, Co, and Ga, indicating a shift due to metamorphic processes. The observed high Cr# (0.68-0.93) and low Mg# (0.25-0.65) values in rims of the altered and porous chromite further illustrate the metamorphic influence on chromite, with greenschist-facies conditions indicated by the Cr-Al-Fe3+ diagram at temperatures below 450 degrees C. The alteration dynamics reflect a progression that initiates with the olivine matrix and advances through reactions involving fresh chromites. This progression results in mass loss, the formation of chlorite, and the porous structures. Our findings contribute to the understanding of metamorphic alteration processes in chromitites and provide a detailed account of the geochemical trends (such as Fe/Mg exchange and trace element enrichment) that reflect greenschist-facies metamorphism. The evidence of chlorite formation and the prevalence of porous textures highlight the influence of metamorphic fluids over serpentinization, offering a model for chromite alteration in supra-subduction zones. This research elucidates the metamorphic history of chromitites in the Kizildag ophiolite.

Uysal, Ibrahim; Sen, Ahmet D.; Su, Ben-Xun; Ersoy, Yalcin; Demir, Yilmaz; Pan, Qi-Qi; Hu, Wen-Jun; Bagci, Utku; Godard, Marguerite

The processes governing ophiolite formation and evolution remain incompletely understood. The K & imath;z & imath;lda & gbreve; ophiolite, a well-preserved remnant of the Neo-Tethyan oceanic lithosphere in the Anatolian region, southern T & uuml;rkiye, offers critical insights into subduction-related processes and geodynamics. This study presents new element data for mineral and whole-rock samples, combined with Re-Os isotopic compositions of mantle peridotites and associated crustal rocks and extrusives. Petrographic observations identify two distinct groups of peridotites: (1) those with very low modal clinopyroxene, interpreted as highly depleted harzburgites and preserving primary mineral assemblages, and (2) depleted harzburgites containing secondary clinopyroxene with elevated trace element contents, inferred to have crystallized from percolating melts and thus reflecting metasomatic modification. Spinel and orthopyroxene compositions indicate 17-25% degrees of partial melting, with evidence for melting in both garnet and spinel stability fields. However, mineral and whole-rock compositions also record subsequent cryptic and modal metasomatism. Crustal rocks and extrusives exhibit geochemical signatures transitional between fore-arc basalts and boninites, consistent with subduction initiation settings. Variations in Os isotope ratios (187Os/188Os) in crustal rocks further reveal melt-rock interactions and the incorporation of radiogenic Os from subducted oceanic crust. The integration of petrographic, geochemical, and isotopic data supports a four-stage tectonic model for subduction initiation and mantle wedge evolution, consistent with global models proposed for supra-subduction zone (SSZ) ophiolites, particularly those of the Tethyan domain. These findings provide new constraints on mantle melting, metasomatism, and subduction initiation processes and contribute to a broader understanding of SSZ mantle evolution in both regional and global contexts.

Uysal, Ibrahim; Akmaz, Recep Melih; Su, Ben-Xun; Demir, Yilmaz; Sen, Ahmet Dundar

The chromitites of the K & imath;z & imath;lda & gbreve; ophiolite (KO) are primarily characterized by massive and disseminated textures within refractory mantle peridotites, predominantly harzburgite and dunite, with occasional occurrences of banded and nodular chromitites. Based on chromite composition, these chromitites can be classified into two groups exhibiting a broad compositional range: intermediate (0.55 <= Cr# < 0.70, TiO2 = 0.08-0.51 wt%) and high-Cr (0.70 <= Cr# <= 0.77, TiO2 = 0.05-0.28 wt%). The compositions of minor and trace elements align consistently with variations in Cr#. Total PGE (Os, Ir, Ru, Rh, Pt, Pd) contents in these chromitites are generally less than 500 ppb, with many samples showing enrichment of IPGE (Os, Ir, Ru) relative to PPGE (Rh, Pt, Pd). However, certain samples from both groups display elevated PGE concentrations (Sigma PGE(intermediate) = 718 ppb, Sigma PGE(High-Cr) = 866 ppb) compared to other samples. The dominant platinum group mineral inclusions in chromite are Ru-rich laurite [(Ru, Os)S-2], with a single osmiridium (Os-Ir alloy) grain also observed suggesting formation under high-temperature and low & fnof;S-2 conditions. Primary base metal mineral inclusions include millerite and pentlandite. Additionally, some chromite crystals contain single or multi-phase silicate inclusions, such as clinopyroxene, orthopyroxene, olivine, and amphibole. Parental melt compositions, calculated from Al2O3 and TiO2 contents of chromites, indicate that most high-Cr chromitites originated from boninitic melts, whereas intermediate chromitites and some high-Cr samples derived from melts with intermediate compositions. Trace element compositions of amphibole and clinopyroxene inclusions in the chromite crystals from the intermediate group further support crystallization from hydrous intermediate melts. It is proposed that the intermediate chromitite group formed from partial melts influenced by fluids from the subducted oceanic crust during the early stages of subduction initiation, while high-Cr chromitites originated from hydrous melts derived from a more depleted mantle wedge in later stages.

Karsli, Orhan; Dokuz, Abdurrahman; Aydin, Faruk; Uysal, Ibrahim; Sengün, Firat; Kandemir, Raif; Santos, Jose Francisco; Andersen, Tom

The initiation of the break-off of the northern branch of the Neotethyan oceanic lithosphere is an important but poorly understood event in the geology of the Sakarya Zone (SZ) in northeastern Turkey. Although it is wellknown that Latest Cretaceous intrusives (-70 Ma) and early Eocene adakitic magmatic rocks are present in the eastern SZ, the outcrops of the early Eocene non-adakitic rocks are very limited, and their tectono-magmatic evolution has not been studied. We describe a small outcrop of non-adakitic quartz diorite porphyry in the Kov area of the Gumushane region in northeastern Turkey. The genesis of these porphyries is significant in evaluating the syn-to post-collision-related magmatism. The LA-ICP-MS zircon U-Pb dating revealed that the Kov quartz diorite porphyries (KQDP) formed at ca. 50 Ma, coeval with adakitic rocks, and-20 Myr later than the slab rollback-related intrusive rocks. The KQDPs are calc-alkaline in composition and enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) and depleted in high field strength elements (HFSEs; e.g., Nb, Ta, Ti), with significant negative anomalies of Nb, Ta, and Ti but positive anomalies of Th, U, and Pb. Isotopic compositions of the samples show limited range of variation and slight enrichment of 87Sr/86Sr(t) (0.70489 to 0.70555), epsilon Nd(t) (-1.4 to -1.2) with TDM of 1.11 to 1.61 Ga. Pb isotopic ratios of the samples point to an enriched mantle source. They were likely crystallized from the melt that originated from an EM2-type spinel-facies subcontinental lithospheric mantle (SCLM), followed by the fractionation with insignificant crustal assimilation. The SCLM was metasomatically enriched, and the metasomatic agent was likely H2O-rich fluids rather than sediments released from subducting oceanic crust during the Late Cretaceous closure of the Neotethyan oceanic lithosphere. In conjunction with the geological background and previous data, we propose that the generation of the KQDPs resulted from a slab break-off event that caused ascending or infiltration of hot asthenosphere, triggering mantle melting. Such sporadic occurrences of the KQDPs, with coeval adakitic rocks in the SZ, are likely associated with the onset of extensional tectonics due to the earlier stage of slab break-off along the region during the early Eocene period.

Karsli, Orhan; Aydin, Faruk; Uysal, Ibrahim; Dokuz, Abdurrahman; Kumral, Mustafa; Kandemir, Raif; Budakoglu, Murat; Ketenci, Murat

An integrated study of comprehensive geochronological, geochemical, and Sr-Nd-Hf isotopic data was undertaken for the A-type Topcam pluton that intruded within the Sakarya Zone (NE Turkey) with the aims of elucidating its origin and tectonic significance and gaining new insights into the generation of aluminous A-type granites. New LA-ICP-MS zircon U-Pb crystallization ages of 72 and 73 Ma indicate emplacement in the Late Cretaceous time, just after extensive metaluminous I-type magmatism in the area. The pluton consists mainly of alkali feldspar, quartz, plagioclase, amphibole, and biotite with accessory minerals such as magnetite, apatite, and zircon. The outcrop is composed of granite, syenite, monzonite, and quartz monzonite and possesses a wide range of SiO2 content (57–70 wt%) with elevated Ga/Al ratios and low Mg# (mostly < 43). The pluton is metaluminous to weakly peraluminous, with aluminium saturation index (ASI) (molar Al2O3/[CaO + K2O + Na2O]) values of 0.82 to 1.18, and belongs to the shoshonitic and ultra-potassic series. All the samples exhibit relative enrichment in light rare earth elements (LREE) and significant negative Eu (Eu/Eu* = 0.31 to 0.86) anomalies on the chondrite-normalized REE diagram. The rocks are enriched in some large ion lithophile elements (e.g., Rb, Th and Ba), and spidergrams show a relative depletion in Nb, Ti, and Sr. The granitic rocks of the pluton have identical 87Sr/86Sr(i) ratios ranging from 0.70518 to 0.70716, relatively low εNd (t) values varying from − 5.5 to − 0.4, and TDM ages (0.82–1.19 Ga). In situ zircon analyses show that the rocks have variable negative and positive εHf (t) values (− 5.5 to 5.9) and Hf two-stage model ages (742 to 1468 Ma), which are indicative of minor addition of juvenile material. Sr-Nd isotope modelling suggests mixing of 70–90% of lower crustal-derived melt with ~ 10–30% of mantle-derived melt at lower crust depths. The heat source for partial melting is provided by upwelling of hot asthenosphere triggered by slab roll-back events. Geochemical and isotopic data reveal that metaluminous A2-type granites were derived from partial melting of the Paleozoic lower continental crust dominated by mafic rocks in amphibolitic composition, with minor input of subcontinental lithospheric mantle-derived magma followed by subsequent limited fractional crystallization to generate a variety of rock types. From integrating all available data with the regional tectonic evolution in the Sakarya Zone and adjacent regions, we attribute generation of aluminous A2-type granites to a back-arc extension in the subduction zone, which is induced by the roll-back of the Neo-Tethyan oceanic slab around 72 Ma. Consequently, we conclude that these A-type granites were related to intensive extension tectonic, which peaked during the late Cretaceous (Maastrichtian) in response to the roll-back of the Neo-Tethyan oceanic slab, which is indicative of the final-stage subduction-related magmatism in the Sakarya Zone.

Uysal, Ibrahim; Dokuz, Abdurrahman; Kapsiotis, Argyrios; Saka, Samet; Karsli, Orhan; Kaliwoda, Melanie; Mueller, Dirk

The eastern Orhaneli ophiolite in NW Anatolia (Turkey) consists of voluminous dunite and minor harzburgite intruded by clinopyroxenite veins. Harzburgite contains spinel of low Cr# [100 x Cr/(Cr + Al) = 40-45] and diopside of low Al2O3 and TiO2 contents, whereas dunite contains spinel of higher Cr# (62-82) and diopside (blebs) (even more) depleted in Al2O3 and TiO2 (than harzburgite). The concentrations of Heavy Rare Earth Elements (HREE) in harzburgite are consistent with derivation of this type of peridotite from 19% dry melting of a fertile mantle protolith at a MOR regime. Dunites have lower concentrations of HREE than harzburgite implying that dunites were generated by higher degrees (> 30%) of (cumulative) melting of the same protolith. Furthermore, the characteristic U-shapes of the chondrite-normalized REE-patterns of dunites indicate the involvement of hydrous melt-peridotite interaction processes in their genesis. Nevertheless, a set of mosaic-in texture dunite samples contain olivine that has lower Fo# [100 x Mg/(Mg + Fe2+)] and NiO contents than olivine in harzburgite. These dunites are probably of cumulate origin as it is also indicated by their enrichment in Pt and Pd (<= 17.92 ppb). Micro-textural and Re-Os isotopic data support that clinopyroxenite intrusions do not have a pure magmatic origin and their formation was partly controlled by metasomatic processes. Overall data indicate that the eastern Orhaneli ultramafic rocks have a complex petrological history including various stages of partial melting, metasomatism and magmatism in an evolving from MOR to SSZ geotectonic setting.

Dokuz, Abdurrahman; Uysal, Ibrahim; Dilek, Yildirim; Karsli, Orhan; Meisel, Thomas; Kandemir, Raif

We report on the structure, geochemistry, Re-Os isotopes and relative abundances of highly siderophile elements (HSEs) of the Paleozoic peridotite-basalt occurrences in the Eastern Pontide belt of northeastern Turkey. These peridotites and the associated basaltic rocks are the remnants of the Rheic oceanic lithosphere, incorporated into the Eurasian continental margin during the Variscan (Hercynian) orogeny. The peridotites display a complex record of multiple magmatic, metasomatic and metamorphic events in different tectonic settings during the evolution of the Rheic upper mantle. The Beyçam harzburgite (BH) contains low Al2O3 (0.51-1.88 anhydrous wt.%) and high MgO (41.35-42.34 wt.%) contents, and its bulk-rock trace element compositions are less than 10% of the primitive upper mantle (PUM) values. The platinum, Pd and Re contents of the Beyçam harzburgite are highly depleted, whereas its Os, Ir, and Ru contents are slightly enriched relative to the PUM values. Its Pd and Re contents that are higher than those of the fertile Pulur lherzolite (PL) to the south and the absence of an isochronous relationship between its 187Os/188Os and 187Re/188Os show that the trace element distribution and the isotope ratios of the Beyçam harzburgite were significantly modified after the first melt-extraction episode. The first melt extraction occurred beneath the Rheic mid-ocean ridge spreading center, whereas the second melt extraction occurred in a mantle wedge above a Rheic subduction zone. The primary magmatic phases of the Pulur lherzolite show the geochemical characteristics typical for fertile lherzolite, formed in the early stages of oceanic lithosphere generation subsequent to the continental break up. The Pulur lherzolite also contains a secondary magmatic phase in the form of networks of clinopyroxene veins and channels, which are interpreted as an evidence for solid state melt-rock reactions between the lherzolite and a percolating basaltic melt above a subduction zone. This clinopyroxene addition resulted in the formation of variable concentrations of Al2O3 (2.47-4.33wt.%) and MgO (29.76-40.10wt.%) in the lherzolite. The rhenium, Pd and Pt concentrations of the Pulur lherzolite are depleted relative to the PUM values, whereas the Os, Ir and Ru concentrations are in the range of the PUM values as commonly observed in peridotites with a melt depletion history. The high suprachondritic 187Os/188Os is, however, inconsistent with a simple melt depletion history, and can be explained by the addition of radiogenic Os-bearing sulfide phases into the lherzolite as a result of melt-rock reactions. Basaltic rocks with an island arc tholeiitic composition from the Beyçam area represent the partial melting product of the moderately depleted Beyçam harzburgite and the basaltic parental melt from which the clinopyroxene precipitated. The covariation between the 187Re/188Os and 187Os/188Os of these basaltic rocks defines an isochron age of 377±8Ma (late Devonian). The combined structural, geochemical and isotope data indicate a prolonged history of multiple episodes of melt extraction-depletion, and melt-rock interaction and fertilization of the mantle lithosphere of the Rheic Ocean.

Uysal, Ibrahim; Şen, A. Dündar; Ersoy, E. Yalçin; Dilek, Yildirim; Saka, Samet; Zaccarini, Federica; Escayola, Monica; Karsli, Orhan

We present the whole-rock and the mineral chemical data for upper mantle peridotites from the Harmanci{dotless}k region in NW Turkey and discuss their petrogenetic-tectonic origin. These peridotites are part of a Tethyan ophiolite belt occurring along the İzmir-Ankara-Ercincan suture zone in northern Turkey, and include depleted lherzolites and refractory harzburgites. The Al2O3 contents in orthopyroxene and clinopyroxene from the depleted lherzolite are high, and the Cr-number in the coexisting spinel is low falling within the abyssal field. However, the orthopyroxene and clinopyroxene in the harzburgites have lower Al2O3 contents for a given Cr-number of spinel, and plot within the lower end of the abyssal field. The whole-rock geochemical and the mineral chemistry data imply that the Harmanci{dotless}k peridotites formed by different degrees of partial melting (~%10-27) of the mantle. The depleted lherzolite samples have higher MREE and HREE abundances than the harzburgitic peridotites, showing convex-downward patterns. These peridotites represent up to ~16 % melting residue that formed during the initial seafloor spreading stage of the Northern Neotethys. On the other hand, the more refractory harzburgites represent residues after ~4-11 % hydrous partial melting of the previously depleted MOR mantle, which was metasomatized by slab-derived fluids during the early stages of subduction. The Harmanci{dotless}k peridotites, hence, represent the fragments of upper mantle rocks that formed during different stages of the tectonic evolution of the Tethyan oceanic lithosphere in Northern Neotethys. We infer that the multi-stage melting history of the Harmanci{dotless}k peridotites reflect the geochemically heterogeneous character of the Tethyan oceanic lithosphere currently exposed along the İzmir-Ankara-Erzincan suture zone.

Karsli, Orhan; Dokuz, Abdurrahman; Kaliwoda, Melanie; Uysal, Ibrahim; Aydin, Faruk; Kandemir, Raif; Fehr, Karl-Thomas

The Eastern Pontides in NE Turkey is one of the major orogenic belts in Anatolia. In this paper, we report our new 40Ar/39Ar dating, mineral chemistry, major and trace elements and Sr-Nd-Pb isotopic analyses of the lamprophyre intrusions in this region. The lamprophyres are widely scattered and intrude Late Carboniferous granitoid rocks. The lamprophyres exhibit fine-grained textures and are mineralogically uniform. Hornblende 40Ar/39Ar dating yielded a plateau age of 216.01±10.64Ma. Based on their geochemistry, mineral compositions and paragenesis, the lamprophyres are classified as calc-alkaline lamprophyres in general and spessartites in particular, which are rich in large ion lithophile elements (e.g., Rb, Ba, K) but depleted in Nb and Ti. Our samples exhibit moderate fractionation in LREE patterns approximately 100 times that of chondrite but HREE abundances less than 10 times that of chondrite. These calc-alkaline lamprophyres display a range of ISr (216Ma) values from 0.70619 to 0.71291 and εNd (216Ma) values from -1.4 to 4.1, with TDM=1.11 to 2.20Ga. Their Pb isotopic ratios indicate an enriched mantle source. The enrichment process is related to metasomatism of a subcontinental lithospheric mantle source, which is caused by a large quantity of H2O-rich fluids, rather than sediments released from oceanic crust at depth during the closure of the Paleotethys Ocean in Triassic times. All of the geochemical data and the trace element modeling suggest that the primary magma of the calc-alkaline to high-K calc-alkaline spessartites was generated at depth by a low degree of partial melting (~1-10%) of a previously enriched lithospheric mantle wedge consisting of phlogopite-bearing spinel peridotite. The ascendance of a hot asthenosphere triggered by extensional events caused partial melting of mantle material. The rising melts were accompanied by fractional crystallization and crustal contamination en route to the surface. All of the geochemical features combined with regional data suggest that the Eastern Pontides calc-alkaline lamprophyres originated in an extensional environment along an active continental margin throughout the Late Triassic. Such an extensional event, causing upwelling of hot asthenosphere, led to the opening of the northern branch of the Neotethys as a back-arc basin farther south of the Eastern Pontides.

Dokuz, Abdurrahman; Uysal, Ibrahim; Siebel, Wolfgang; Turan, Mehmet; Duncan, Robert; Akçay, Miǧraç

New geochemical and isotopic data for post-collisional Early Eocene and Late Miocene adakitic rocks from the eastern part of the Sakarya Zone, Turkey, indicate that slab and lower crustal melting, respectively, played key roles in the petrogenesis of these rocks. The Early Eocene Yoncali{dotless}k dacite (54.4 Ma) exhibits high Sr/Y and La/Yb ratios, low Y and HREE concentrations, moderate Mg# (44-65), and relatively high εNd and low ISr values, similar to adakites formed by slab melting associated with subduction. Geochemical composition of the Yoncali{dotless}k dacite cannot be explained by simple crystal fractionation and/or crustal contamination of andesitic parent magma, but is consistent with the participation of different proportions of melts derived from subducted basalt and sediments. Sr/Y correlates horizontally with Rb/Y, and Pb/Nd correlates vertically with Nd isotopic composition, indicating that Sr and Pb budgets are strongly controlled by melt addition from the subducting slab, whereas positive correlations between Th/Nd and Pb/Nd, and Rb/Y and Nb/Y point to some contribution of sediment melt. In addition to low concentrations of heavy rare earth elements (~2-3 times chondrite), a systematic decrease in their concentrations and Nb/Ta ratios with increasing SiO2 contents suggests that slab partial melting occurred in the garnet stability field and that these elements were mobilized by fluid flux. These geochemical and isotopic signatures are best explained by slab breakoff and fusion shortly after the initiation of collision. Although the Late Micone Tavdaǧi{dotless} rhyolite (8.75 Ma) has some geochemical features identical to adakites, such as high Sr/Y and La/Yb ratios, low Y and HREE concentrations, other requirements, such as sodic andesite and/or dacite with relatively high MgO and Mg# (>50), relatively high Ni and Cr, low K2O/Na2O (<0.4), high Sr (>400 ppm), for slab-derived adakites are not provided. It is sodic in composition and shows no traces of fractionation from dacitic parent magma. Low Nd and high Sr isotope ratios suggest derivation by partial fusion of calc-alkaline, juvenile crust with high Sr/Y and La/Yb ratios.

Uysal, Ibrahim; Ersoy, E. Yalcin; Karsli, Orhan; Dilek, Yildirim; Sadiklar, M. Burhan; Ottley, Chris J.; Tiepolo, Massimo; Meisel, Thomas

We present new, whole-rock major and trace element chemistry, including rare earth elements (REE), platinum-group elements (PGE), and Re-Os isotope data from the upper mantle peridotites of a Cretaceous Neo-Tethyan ophiolite in the Mugla area in SW Turkey. We also report extensive mineral chemistry data for these peridotites in order to better constrain their petrogenesis and tectonic environment of formation. The Mugla peridotites consist mainly of cpx-harzburgite, depleted harzburgite, and dunite. Cpx-harzburgites are characterized by their higher average CaO (2.27 wt.%), Al2O3 (2.07 wt.%), REE (53 ppb), and Os-187/Os-188((i)) ratios varying between 0.12497 and 0.12858. They contain Al-rich pyroxene with lower Cr content of coexisting spinel (Cr# = 13-22). In contrast, the depleted harzburgites and dunites are characterized by their lower average CaO (0.58 wt.%), Al2O3 (0.42 wt.%), and REE (1.24 ppb) values. Their clinopyroxenes are Al-poor and coexist with high-Cr spinel (Cr# = 33-83). The Os-187/Os-188((i)) ratios are in the range of 0.12078-0.12588 and are more unradiogenic compared to those of the cpx-harzburgites. Mineral chemistry and whole rock trace and PGE data indicate that formation of the Mugla peridotites cannot be explained by a single stage melting event; at least two-stages of melting and refertilization processes are needed to explain their geochemical characteristics. Trace element compositions of the cpx-harzburgites can be modeled by up to similar to 10-16% closed-system dynamic melting of a primitive mantle source, whereas those of the depleted harzburgites and dunites can be reproduced by similar to 10-16% open-system melting of an already depleted (similar to 16%) mantle. These models indicate that the cpx-harzburgites are the products of first-stage melting and low-degrees of melt-rock interaction that occurred in a mid-ocean ridge (MOR) environment. However, the depleted harzburgites and dunites are the product of second-stage melting and related refertilization which took place in a supra subduction zone (SSZ) environment. The Re-Os isotope systematics of the Mugla peridotites gives model age clusters of similar to 250 Ma, similar to 400 Ma and similar to 750 Ma that may record major tectonic events associated with the geodynamic evolution of the Neo-Tethyan. Rheic, and Proto-Tethyan oceans, respectively. Furthermore, >1000 Ma model ages can be interpreted as a result of an ancient melting event before the Proto-Tethys evolution. (C) 2011 Elsevier B.V. All rights reserved.

Dokuz, Abdurrahman; Uysal, Ibrahim; Kaliwoda, Melanie; Karsli, Orhan; Ottley, Chris J.; Kandemir, Raif

The boundary between the Gondwana and Laurussia, or a terrane separated from it, is traced by a suture recording the closure of the Rheic ocean in the Pulur, Beyçam and Kurtoǧlu areas of the eastern Sakarya Zone of Turkey. Pulur lherzolite has a lower Cr# [100Cr/(Cr+Al)=5-37] of the spinel and slightly enriched flat medium-heavy rare earth element (M-HREE) whole-rock pattern typical for those of the fertile abyssal-type lherzolite. By contrast, the Beyçam harzburgite displays the mineralogical and geochemical features of a moderately depleted residue at a supra subduction zone (SSZ). Some of spinels from the Beyçam peridotites show TiO2 contents (0.15-0.48wt.%) identical to a later interaction with a melt of island-arc tholeiite (IAT) composition. Meta-basalt from the Beyçam area is the representative of such a melt and displays the whole-rock M-HREE pattern of a complementary product of the Beyçam harzburgite. Data presented in this study support the primarily northward directed closure of the Rheic ocean, but suggest that the Variscan basement in the eastern part of the Sakarya Zone consists of mantle peridotites formed in a south-vergent SSZ. This dual polarity of subduction in the Rheic ocean, at least in the second half of its closure, is also favored by the geological structure and lithological diversity of the Variscan rocks. These are: (1) spatial distribution of the peridotites, e.g., SSZ-type harzburgites to the north and abyssal-type lherzolites to the south, (2) lack of high-pressure metamorphic rocks, (3) decrease in the degree of Variscan metamorphism toward the north, and (4) emplacement of Variscan syn-collisional magmatism into the low grade metamorphic rocks to the north. Paleotethys was the other ocean of the region created in the Late Paleozoic. Northward subduction of the Rheic ocean from Early Devonian to Early Carboniferous appears to be the most plausible mechanism responsible for the opening of Paleotethys. In this scenario the Paleotethys is envisaged as a back-arc basin opened to the north in the wake of separated terranes from Laurussia. Onset of trench-Rheic mid-ocean ridge collision in the Early Devonian along the northern margin of Laurussia has been proposed to account for the initiation of SSZ-type subduction to the south. The short duration of this subduction appears insufficient to open a fully developed back-arc basin to the south because the elimination of Rheic mid-ocean ridge to the north accelerated the oceanic closure.

Karsli, Orhan; Ketenci, Murat; Uysal, Ibrahim; Dokuz, Abdurrahman; Aydin, Faruk; Chen, Bin; Kandemir, Raif; Wijbrans, Jan

The tectonic setting of the Eastern Pontides during the late Mesozoic to early Cenozoic remains a subject of debate. Petrogenesis of adakite-like granitoid porphyries plays a critical role in determining the nature of the lower continental crust and mantle dynamics during orogenic processes in the region. Here we describe, for the first time, the late Paleocene to early Eocene adakite-like granitoid porphyries from the northern part of the Eastern Pontides although their counterparts in the southern part have recently been found. The adakitic porphyries, which emplaced into the subduction-related Turonian-Santonian volcanics from northern part of the region, consist of I-type calc-alkaline quartz monzonite-tonalite (SiO2 = 62.89-65.07 wt.%) and high-k calc-alkaline granodiorite-granite associations (SiO2 = 69.06-70.43 wt.%). The former displays peraluminous to metaluminous signatures, whereas the latter shows peraluminous geochemical character. The granite-granodiorite porphyries have high K2O (3.32-3.84 wt.%), and low Na2O (3.48-4.61 wt.%) and MgO (0.91-1.04 wt.%) relative to the quartz monzonite-tonalite association (K2O = 1.50-1.92 wt.%; Na2O = 4.08-6.45 wt.%; MgO = 1.44-2.07 wt.%). Ar-Ar geochronology studies on the amphibole separates reveal that the adakite-like porphyries have a crystallization ages of 51.34 +/- 0.27 to 53.55 +/- 0.34 Ma. Here, we contend that these rocks were formed by partial fusion of a mafic lower continental crust in a collisional phase but not in a subduction setting. All the samples exhibit the typical geochemical characteristics of adakite, that is, high Sr (250-1141 ppm), high Sr/Y ratios (16-147), low Y (6.8-14.8 ppm) and low HREE concentrations; they are similar to adakites formed by slab melting associated with the subduction zone. However, the rocks exhibit heterogeneity in isotopic composition, with I-Sr ranging from 0.70554 to 0.70986, epsilon(Nd) (51 Ma) from -8.5 to -0.9 and Nd model ages from 0.72 to 1.26 Ga. The samples are characterized by relatively high Th, Th/U and no significant Eu anomalies, implying that garnet was stable in their source during partial melting. The compositional diversity between rock groups is probably related to partial melting of heterogeneous lower crustal source. All of the features are inconsistent with a slab-melting origin and slab-related petrogenetic model, but instead, they favor an origin by melting of heterogeneous lower continental crust due to a thermal anomaly that was induced by the upwelling of the asthenosphere through a slab break-off in a collisional setting. These interpretations argue against the evidence for the presence of an early Cenozoic arc setting in the Eastern Pontides. Instead, the early Cenozoic time in the region may be attributed to a geodynamic response to a post-collisional uplift phase that occurred along the continent-continent collision between the Pontide and the Anatolide-Tauride blocks. (C) 2011 Elsevier B.V. All rights reserved.

Karsli, Orhan; Dokuz, Abdurrahman; Uysal, Ibrahim; Aydin, Faruk; Kandemir, Raif; Wijbrans, Jan

Early Cenozoic (48-50 Ma) adakitic volcanic rocks from the Eastern Pontides, NE Turkey, consist of calc-alkaline and high-K calc-alkaline andesite and dacite, with SiO2 contents ranging from 56.01 to 65.44 wt.%. This is the first time that Early Eocene volcanism and adakites have been reported from the region. The rocks are composed of plagioclase, amphibole, quartz, and Mg-rich biotite. They have high and low-Mg# values ranging from 55 to 62 and 13 to 42, respectively. High-Mg# rocks have higher Ni and Co contents than low-Mg# samples. The rocks exhibit enrichments in large ion lithophile elements including the light rare earth elements, depletions in Nb, Ta and Ti and have high La/Yb and Sr/Y ratios. Their relative high ISr (0.70474-0.70640) and low εNd (50 Ma) values (- 2.3 to 0.8) are inconsistent with an origin as partial melts of a subducted oceanic slab. Combined major- and trace element and Sr-Nd isotope data suggest that the adakitic magmas are related to the unique tectonic setting of this region, where a transition from a collision to an extension stage has created thickening and delamination of the Pontide mafic lower crust at 50 Ma. The high-Mg adakitic magmas resulted from partial melting of the delaminated eclogitic mafic lower crust that sank into the relatively hot subcrustal mantle, and its subsequent interaction with the mantle peridotite during upward transport, leaving garnet as the residual phase, elevates the MgO content and Mg# of the magmas, whereas low-Mg# magmas formed by the melting of newly exposed lower crustal rocks caused by asthenospheric upwelling, which supplies heat flux to the lower crust. The data also suggest that the mafic lower continental crust beneath the region was thickened between the Late Cretaceous and the Late Paleocene and delaminated during Late Paleocene to Early Eocene time, which coincides with the initial stage of crustal thinning caused by crustal extensional events in the Eastern Pontides and rules out the possibility of an extensional regime before ~ 50 Ma in the region during the Late Mesozoic to Early Cenozoic.

Karsli, Orhan; Dokuz, Abdurrahman; Uysal, Ibrahim; Aydin, Faruk; Chen, Bin; Kandemir, Raif; Wijbrans, Jan

We present elemental and Sr-Nd-Pb isotopic data for the magmatic suite (~79 Ma) of the Harşit pluton, from the Eastern Pontides (NE Turkey), with the aim of determining its magma source and geodynamic evolution. The pluton comprises granite, granodiorite, tonalite and minor diorite (SiO2 = 59.43-76.95 wt%), with only minor gabbroic diorite mafic microgranular enclaves in composition (SiO2 = 54.95-56.32 wt%), and exhibits low Mg# (<46). All samples show a high-K calc-alkaline differentiation trend and I-type features. The chondrite-normalized REE patterns are fractionated [(La/Yb)n = 2.40-12.44] and display weak Eu anomalies (Eu/Eu* = 0.30-0.76). The rocks are characterized by enrichment of LILE and depletion of HFSE. The Harşit host rocks have weak concave-upward REE patterns, suggesting that amphibole and garnet played a significant role in their generation during magma segregation. The host rocks and their enclaves are isotopically indistinguishable. Sr-Nd isotopic data for all of the samples display ISr = 0.70676-0.70708, εNd(79 Ma) = -4.4 to -3.3, with TDM = 1.09-1.36 Ga. The lead isotopic ratios are (206Pb/204Pb) = 18.79-18.87, (207Pb/204Pb) = 15.59-15.61 and (208Pb/204Pb) = 38.71-38.83. These geochemical data rule out pure crustal-derived magma genesis in a post-collision extensional stage and suggest mixed-origin magma generation in a subduction setting. The melting that generated these high-K granitoidic rocks may have resulted from the upper Cretaceous subduction of the Izmir-Ankara-Erzincan oceanic slab beneath the Eurasian block in the region. The back-arc extensional events would have caused melting of the enriched subcontinental lithospheric mantle and formed mafic magma. The underplating of the lower crust by mafic magmas would have played a significant role in the generation of high-K magma. Thus, a thermal anomaly induced by underplated basic magma into a hot crust would have caused partial melting in the lower part of the crust. In this scenario, the lithospheric mantle-derived basaltic melt first mixed with granitic magma of crustal origin at depth. Then, the melts, which subsequently underwent a fractional crystallization and crustal assimilation processes, could ascend to shallower crustal levels to generate a variety of rock types ranging from diorite to granite. Sr-Nd isotope modeling shows that the generation of these magmas involved ~65-75% of the lower crustal-derived melt and ~25-35% of subcontinental lithospheric mantle. Further, geochemical data and the Ar-Ar plateau age on hornblende, combined with regional studies, imply that the Harşit pluton formed in a subduction setting and that the back-arc extensional period started by least ~79 Ma in the Eastern Pontides.

Dokuz, Abdurrahman; Karsli, Orhan; Chen, Bin; Uysal, Ibrahim

Small granitoids emplaced into the early Jurassic volcani-clastic succession in the Yusufeli area, northeastern Turkey, can be temporally and geochemically classified into two groups: early Jurassic low-K and late Jurassic high-K. 40Ar-39Ar hornblende analyses yielded 188.0 ± 4.3 Ma for the Dutlupi{dotless}nar intrusion, dating the subduction related rifting in the region. It comprises metaluminous to weakly peraluminous (ASI = 0.94-1.11) granodiorite and, to a lesser extent, tonalite whose K2O-poor (< 2.04 wt.%) nature and weak negative Eu anomalies (Eu/Eu* = 0.9-0.7) preclude derivation by fractional crystallization from a K-rich melt. Sr, Nd and Pb isotopic data reveal derivation by partial melting from an already cooled tholeiitic basic rocks which had mantle-like isotope signature. The Sumbated intrusion formed in the late Jurassic (153.0 ± 3.4 Ma) and consists chiefly of metaluminous (ASI = 0.84-0.99) quartz monzodiorite. Medium to high-K2O, relatively high MgO and Sr contents, flat HREE patterns without prominent Eu anomalies, slightly positive εNd(t) values (+ 1.5 to + 2.5) and low ISr ratios (0.7046-0.7056) are consistent with an origin by dehydration melting of a juvenile source, above the garnet stability field, dominated by likely K-amphibole bearing calc-alkaline mafic rocks. Geochemical data show that fractional crystallization from a Sumbated-like quartz monzodioritic magma is the fundamental process responsible for the evolved compositional range of the Keçikaya intrusion. The geochemical and geochronological data presented here indicate that the late Jurassic magmatism occurred in a post-collisional setting. Slab-breakoff, which was followed by shortly after collision, seems to be the most plausible mechanism for the generation of medium to high-K calc-alkaline rocks of the Sumbated and the Keçikaya intrusions, indicating a switch in the geodynamic setting, e.g., from pre-collision to post-collision in the middle Jurassic in the eastern Pontides.

Demir, Yilmaz; Uysal, Ibrahim; Sadiklar, M. Burhan; Sipahi, Ferkan

Vein type Köstere ores were deposited along cracks formed as a result of NE-SW fault system in the late Cretaceous felsic volcanic rocks in the northeastern Black Sea Region of Turkey. Total silver content of the Köstere ore is controlled by total silver content of the hydrothermal solution, homogenization temperature of the ore minerals and modal abundances of the tetrahedrite-tennantite serie minerals. The Zn/Cd ratios of sphalerites from the Köstere deposit are close to those of granite-related classical vein-type hydrothermal deposits. Furthermore Co/Ni ratio in pyrite separates, higher than unit, suggests an acidic source for the ore forming fluids. Homogenization temperatures of 200-370 °C and salinity of 0-9.85 eq. wt% NaCl were obtained on the basis of fluid inclusions studies measured in quartz minerals. These data indicate that ore formation conditions for the Köstere ore are similar with the vein-type epithermal-mesothermal deposits, related to the magmatic fluids. The overall low salinities of fluids (on average: 5.4 eq. wt% NaCl) suggest that meteoric waters were involved in mineralization. The possibility of interactions between ascending hydrothermal fluids and dilute meteoric waters is supported by geological features and mineralogical data which indicate a shallow depth of mineralization. Torul Pluton, which is the younger acidic unit (72 my) in the area, is suggested to be related to the formation of Köstere deposit.

Karsli, Orhan; Chen, Bin; Uysal, Ibrahim; Aydin, Faruk; Wijbrans, Jan R.; Kandemir, Raif

Whole-rock geochemical and Sr, Nd and Pb isotope data are presented for a representative suite of the Quaternary Erzincan Volcanics (QEV) from the Erzincan basin (EB) along the North Anatolian Fault Zone, aiming to understand their origin and implications for basalt-lower crust interaction. Unspiked K-Ar and 40Ar/39Ar dating of dome lavas from the QEVs yielded ages of 102 ± 2 to 1061 ± 88 ka. The QEVs range from high-K low silica trachy-andesite to rhyolite in composition, with rhyolite volumetrically the most abundant. All rocks show high-K calc-alkaline affinity, a geochemical signature common to many post-collisional magmas. They are characterized by enrichment in LILE (Rb, Ba, K, Th) and LREE ((La/Yb)CN = 3-33), with pronounced depletion of HFSE. All lavas show negligible or small negative Eu anomalies in the andesitic to dacitic and strong Eu anomalies in the rhyolitic samples. These rocks have relatively low 87Sr/86Sr = 0.70404-0.70587 and slightly depleted Nd isotopic compositions (εNd from - 0.9 to 2.8), with significantly varied Mg# ranging from 2 to 53. Pb isotopic compositions [206Pb/204Pb = 18.90-19.02, 207Pb/204Pb = 15.64-15.70, 208Pb/204Pb = 38.91-39.97] reveal an enriched source signature, which implies that some portions of metasomatized lithospheric mantle could have contributed to their genesis. The isotopic ratios and chemical features along with the textural and compositional disequilibrium of the plagioclases and amphiboles suggest that mixing of mafic and felsic magmas played an important role in the magma genesis. A possible scenario for the genesis of these volcanic rocks is that basaltic magma formed as a result of partial melting of a subcontinental lithospheric mantle source responding to a possible upwelling of asthenospheric mantle which was caused by the extension produced by strike-slip tectonics. Underplating of these high-temperature basaltic magmas sparked partial fusion of a juvenile lower continental crust producing felsic melts; then magma mixing between basaltic and the felsic magmas followed. Fractional crystallization, with minor amounts crustal contamination could have played an important role in the evolution of magma. Modelling based on Sr and Nd isotope data shows that less than 10% of a basic magma and about 90% of juvenile lower continental crustal material was involved in the generation of the QEVs in a pull-apart basin along the North Anatolian Fault Zone.

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

Magnetite-ulvöspinel and ilmenite-hematite solid solution intergrowths from the high-K calc-alkaline Dölek and Sarιçiçek 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 ulvöspinel 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 Mt98-70Usp02-30 and Ilm99-65Hm01-35 in composition, respectively. Estimations of oxygen fugacity and temperature using the titanomagnetite-ilmenite thermometry/oxygen barometry range from log/O2 of -15.30 to -20.48 in host rocks, log/O2 of -15.39 to -20.80 in the mafic microgranular enclaves and 617±6 to 758±23 °C in host rocks, 622±6 to 735±24 °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 °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 invarious proportion 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 result in thermal perturbation and melting of lithospheric mantle. Intrusion of hot lithospheric mantle-derived mafic magma then induced lower crustal melting, producing felsic melt. Mixing of the lower crust-derived melt and lithospheric mantle-derived magma formed the hybrid pluton. This process requires a post-collisional extensional tectonic setting during the Eocene in the Eastern Pontides.