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Chromite, ultramafic and mafic rocks from Eldivan, Yapraklı, Ayli Dağ, Küre, Elekdağ and Kızılırmak in northern Turkey have been studied to determine their mineral and whole-rock geochemical, and Re-Os isotope geochemical characteristics. Most of the studied peridotites display depleted but commonly V-shaped chondrite-normalized rare-earth element (REE) patterns while some peridotites as well as pyroxenites from all areas exhibit light REE depleted patterns. Olivine (forsterite 82 to 92 mol%) and spinel (chromium number 13 to 63) in the studied peridotites exhibit a wide range of compositions. Compositions of spinels suggest that peridotites from Eldivan, Ayli Dağ and Küre experienced relatively large degrees of partial melting (~ 15 and 19 wt%), whereas those of the Kızılırmak area most likely reflect lower melting degrees (~ 4–6 wt%). Whole-rock and mineral chemical data indicate that the ultramafic rocks are similar to abyssal and supra-subduction zone peridotites. The ultramafic rocks of the investigated areas exhibit a wide range of 187Re/188Os (0.12 to 6.6) and measured 187Os/188Os (0.122–1.14), while the basaltic rocks from Küre, Eldivan and Kızılırmak areas have high 187Re/188Os (128–562) and measured 187Os/188Os (0.724–1.943). On the other hand, chromite from Eldivan, Elekdağ and Kızılırmak show high Os contents (21.81–44.04 ppb) and low 187Re/188Os (0.015–0.818) and 187Os/188Os (0.122–0.133). Re-Os model ages (TChur) for all analyzed samples yielded scattered ages ranging from Jurassic to Proterozoic. Overall, geochemical data are interpreted to reflect different degrees of partial melting, melt – rock interactions and metasomatic effects that produced a heterogeneous mantle in a supra-subduction setting. [ABSTRACT FROM AUTHOR]

Mafic and felsic igneous rocks in the Karacaali Magmatic Complex (KMC) in the northwestern margin of the Central Anatolian Crystalline Complex (CACC) are classified into 4 groups: i) granitoid pluton including granite, granodiorite, and monzonite; ii) a few meter-scale porphyritic microgranite enclaves within the hybrid rocks; iii) hybrid rocks formed by mixing/mingling of mafic lavas (basaltic/diabasic/lamprophyric), anorthositic, and/or rhyolitic lavas; iv) diabasic dykes/veins within the granitoid pluton. Major element composition of the granitoid pluton and porphyritic microgranite enclaves within the hybrid rocks indicate subalkaline, calc-alkaline, and mostly I-type characteristics. These rocks are mainly peraluminous with aluminum saturation index > 1, but mainly between 1 and 1.1, indicating transitional peraluminous. On the tectonomagmatic discrimination diagrams (Y vs. Nb and (Y+Nb) vs. Rb diagrams), all the granitic and monzonitic rock suites from the complex fall mostly in the VAG+Syn-COLG and VAG fields respectively, suggesting arc-related origin. On the R1 vs. R2 tectonic diagram, the granitic rocks display distribution from preplate collision to syncollision field, but quartz-monzonitic samples plot within the postcollision uplift field. Based on limited geological, petrographic, and geochemical results, the tectonomagmatic evolution of the KMC can be summarized as follow: i) initiation of subduction of the Inner Tauride oceanic lithosphere beneath the CACC during the Late Cretaceous time; ii) underplating of partial melts derived from subducted slab and/or mantle wedge, which provided enough heat for partial melting of the mafic lower crust and generation of granitic magma; iii) slab detachment following the continent-continent collision that resulted in tensional forces within the overlying continental crust, which allowed the intrusion of the granitic magma to the upper crust, also cutting the central Anatolian ophiolites, from the Late Cretaceous to most likely the Paleocene time. The hybrid rocks formed by mixing/mingling of the mafic, anorthositic, and/or rhyolitic magmas most likely indicate their injection into a partly crystalline granitic magmatic system just after crystallization of granitic magma in the upper crust. However, this model is open to discussion and needs to be investigated using isotope data in future studies. [ABSTRACT FROM AUTHOR]

The Pozantı-Karsantı ophiolite consists of a mantle unit and overlying crustal rocks. The mantle peridotite is composed of harzburgitic to dunitic rocks that are depleted in Al2O3 and CaO compared to primitive mantle. The low whole-rock Al and Ca values are consistent with the high Cr# [= 100 x Cr/(Cr + Al)] values of spinel that range from 44 to 70. These spinels generally have low TiO2 (< 0.06 wt.%) concentrations, although spinels with high-Cr compositions in certain samples exhibit enrichments of up to 0.16 wt.% TiO2. The concentrations of chondrite-normalized rare earth elements (REEs) indicate depletion toward heavy to middle REEs. However, the entire mantle peridotite samples exhibit marked enrichment in light REEs and large-ion lithophile elements (LILEs) compared to middle REEs. The heavy REE patterns of some peridotite samples are comparable to the calculated melting curves representing various degrees of melting and are modeled by ~ 24% to 30% melting in the spinel stability field. However, some samples are more depleted in the middle REEs than heavy REEs. The patterns of heavy to middle REEs do not follow the melting lines produced by various degrees of melting in the spinel stability field. The heavy REE composition of these peridotite samples suggests that partial melting began in the garnet stability field and continued into the spinel stability field; they represent ~ 22% to 26% melting under various pressure conditions. High anorthite content of plagioclase as well as Nb-depleted composition of mafic cumulates and isotropic gabbros indicate that the crustal rocks of the Pozantı-Karsantı ophiolite formed from a melt that has been produced by melting of depleted source. This melt is thought to have enriched in light REE and fluid mobile elements that were released from the subducting slab during the subduction of Neotethyan ocean. The whole-rock light REE and LILE enrichments and the higher TiO2 concentrations of the high-Cr# spinels in some mantle peridotite samples cannot be explained by simple melt extraction in a mid-ocean ridge (MOR) environment and require melting and enrichment processes in a supra-subduction zone tectonic setting. However, these features of the peridotites can be explained by the interaction of light REEs and TiO2-rich melts and fluids with peridotites that were depleted during melting events in an MOR environment. This interaction, took place in a supra-subduction zone environment, may have increased the light REE concentrations in the peridotites and caused the re-equilibration of the Ti-depleted spinel to produce Ti-richer spinel and therefore explains the geochemical signatures of the Pozantı-Karsantı peridotites. [ABSTRACT FROM AUTHOR]

Abstract: The volcanic activity of Mt. Karacadağ (SE Anatolia) is divided into three major stages: Siverek Stage (∼11–2.7Ma), Karacadağ Stage (∼1.9–1.0Ma) and Ovabağ Stage (0.4–0.01Ma). The magmas are mildly alkaline mafic rocks, mostly basanites, hawaiites and alkali basalts. Detailed geochemical investigation indicates a continuous variation of composition with time, with the oldest products (Siverek Stage) being characterized by average lowest HFSE (Ti, Hf, Zr, Nb, Ta), 143Nd/144Nd, Nb/U, Ta/Yb, Nb/Nb* and the highest ΔQ, La/Nb, Ti/Nb, Zr/Nb, Ba/Nb, Th/Ta, K/La, and the youngest products (Ovabağ Stage) at the opposite end of the trend. The overall incompatible element content of the Karacadağ volcanic rocks resembles closely average HIMU-OIB compositions, with the oldest samples deviating more strongly from typical compositions of “anorogenic” magmas. We interpret these geochemical variations with a process of partial melting of a chemically and mineralogically heterogeneous mantle source rather than with process of variable crustal contamination at shallow depths. During the first stages of mantle melting the volumes with lowest solidus temperature (e.g., the amphibole and phlogopite-rich metasomes, particularly abundant in the Arabia mantle xenolith suite) contributed significantly to the partial melts. “Average” peridotitic matrix is involved in partial melting processes only when these metasomatic volumes start to be exhausted, producing mantle melts with geochemical composition resembling average “anorogenic” mildly alkaline sodic rocks, common in the circum-Mediterranean area. [Copyright &y& Elsevier]

Abstract: Eastern Anatolia consisting of an amalgamation of fragments of oceanic and continental lithosphere is a current active intercontinental contractional zone that is still being squeezed and shortened between the Arabian and Eurasian plates. This collisional and contractional zone is being accompanied by the tectonic escape of most of the Anatolian plate to the west by major strike-slip faulting on the right-lateral North Anatolian Transform Fault Zone (NATFZ) and left-lateral East Anatolian Transform Fault Zone (EATFZ) which meet at Karlıova forming an east-pointing cusp. The present-day crust in the area between the easternmost part of the Anatolian plate and the Arabian Foreland gets thinner from north (ca 44 km) to south (ca 36 km) relative to its eastern (EAHP) and western sides (central Anatolian region). This thinner crustal area is characterized by shallow CPD (12–16 km), very low Pn velocities (<7.8 km/s) and high Sn attenuation which indicate partially molten to eroded mantle lid or occurrence of asthenospheric mantle beneath the crust. Northernmost margin of the Arabian Foreland in the south of the Bitlis–Pötürge metamorphic gap area is represented by moderate CPD (16–18 km) relative to its eastern and western sides, and low Pn velocities (8 km/s). We infer from the geophysical data that the lithospheric mantle gets thinner towards the Bitlis–Pötürge metamorphic gap area in the northern margin of the Arabian Foreland which has been most probably caused by mechanical removal of the lithospheric mantle during mantle invasion to the north following the slab breakoff beneath the Bitlis–Pötürge Suture Zone. Mantle flow-driven rapid extrusion and counterclockwise rotation of the Anatolian plate gave rise to stretching and hence crustal thinning in the area between the easternmost part of the Anatolian plate and the Arabian Foreland which is currently dominated by wrench tectonics. [Copyright &y& Elsevier]