Chromitite deposits of Turkey in Tethyan ophiolites

Some parts of the Tethyan ophiolites of Alpine-Himalayan suture belt are located within Turkey. The Tethyan belt splits into two branches in Turkey. The northern branch follows the İzmir-Ankara-Erzincan Zone, while the southern branch extends along the Anatolide-Tauride and Bitlis-Zagros suture zone. The subsections of the latter reach Iran in the east and Oman ophiolites in the south east. These ophiolites are also the only environments in which chromitite deposits occur. Consequently, the ophiolites in Turkey are significantly rich in terms of Alpine type chromitite occurrences and they are the oldest metallic mine products. There has been chromitite ore production in Turkey since the nineteenth century. With their refractory quality, chromitite produced in Turkey has always had a good standing in the market. Chromitite, which was exported as lump ore until mid-twentieth century, started to be used in the domestic market as the country’s industry developed, but still, even today an important part of the production is exported. In addition, since the chromitite developments near to the surface are almost completely exhausted, the chromitite ore production in the country has evolved to concentrated ore obtained from low grade deposits, through beneficiation. Although there are many active beneficiation plants in various parts of the country, there is still a significant amount of concentrate ore production; especially in the deposits of Adana-Aladağ region. In this chapter, the mentioned chromitite occurrences are discussed in a specific order from west to east, taking into account the ophiolite sequences to which they belong. The North Anatolian Ophiolites are introduced in the first three sections whereas the other three sections present the chromitite deposits of the South Anatolian Ophiolites. Nevertheless, considering the historical records and future production potentials, Turkey’s most important chromitite production regions could be listed in order of priority as Guleman (Elazığ), Kopdağ region (Erzincan), Muğla-Fethiye region, Aladağ-Pınarbaşı (Adana-Kayseri), Orhaneli-Harmancık (Bursa)-Eskişehir region and Hatay. It is clear that these should all be taken into consideration for further prospecting targeting. © Springer Nature Switzerland AG 2019

Permo-Carboniferous granitoids with Jurassic high temperature metamorphism in Central Pontides, Northern Turkey

In the northern part of the Central Pontides (N Turkey) there are different metamorphic rocks exposed, notably the Devrekani metamorphic rocks. Here, upper amphibolite-lower granulite facies metamorphic rocks contain predominantly paragneiss, orthogneiss and metacarbonate, and to a lesser extent, amphibolite and quartzite, with cross-cutting aplite, pegmatite and granite veins. This is the first report of these rocks and includes new data on the petrochemistry, geochronology and metamorphic evolution of the Devrekani orthogneisses from the Central Pontides. The orthogneisses show five different mineral parageneses with the characteristic mineral assemblage quartz + K-feldspar + plagioclase + biotite ± hornblende ± opaque (± ilmenite and ± magnetite), and accessory minerals (zircon, sphene and apatite). These metamorphic rocks exhibit generally granoblastic, lepidogranoblastic and nematolepidogranoblastic with locally migmatitic and relic micrographic textures. They have well-developed centimeter-spaced gneissic banding and display gneissose structure with symmetric, asymmetric and irregular folds. The petrographic features, mineralogical assemblages and weak migmatization reflect high temperature conditions. Thermometric calculations in the orthogneisses indicate metamorphic temperatures reached 744 ± 33 °C. Field relations, petrography and petrochemistry suggest that the orthogneisses have predominantly granodioritic and some granitic protoliths, that show features of I-type, medium to high-potassic calc-alkaline volcanic arc granitoids. The orthogneisses have high contents of LILEs and low contents of HFSEs with negative Nb and Ti anomalies, which are typical of subduction-related magmas. The orthogneisses also show significant LREE enrichment relative to HREE with negative Eu anomalies (EuN/Eu* = 0.33–1.07) with LaN/LuN = 6.98–20.47 values. Based on U-Pb zircon dating data, the protoliths are related to Permo-Carboniferous (316–252 Ma) magmatism. It is likely that peak metamorphism took place during the Jurassic as reflected by the U-Pb zircon ages (199–158 Ma) and also 40Ar/39Ar from hornblende/biotite (163–152 Ma). The four biotite 40Ar/39Ar average ages from the rock samples are ca. 156 Ma, suggesting that the metamorphic rocks cooled to 350–400 °C at ca. 156 Ma. Conclusively, the Devrekani metamorphic rocks can be ascribed as products of Permo-Carboniferous continental arc magmatism overprinted by Jurassic metamorphism in the northern Central Pontides

Neotethyan closure history of western Anatolia: a geodynamic discussion

International audienceThis paper addresses the lithosphere-scale subduction–collision history of the eastern termination of the Aegean retreating subduction system, i.e. western Anatolia. Although there is some general consensus on the protracted subduction evolution of the Aegean since the early Cenozoic at least, correlation with western Anatolia has been widely debated for more than several decades. In western Anatolia, three main tectonic configurations have been envisaged in the past years to reconstruct slab dynamics during the closure of the Neotethyan oceanic realm since the Late Cretaceous. Some authors have suggested an Aegean-type scenario, with the continuous subduction of a single lithospheric slab, punctuated by episodic slab roll-back and trench retreat, whereas others assumed a discontinuous subduction history marked by intermittent slab break-off during either the Campanian (ca. 75 Ma) or the Early Eocene (ca. 55–50 Ma). The third view implies three partly contemporaneous subduction zones. Our review of these models points to key debated aspects that can be re-evaluated in the light of multidisciplinary constraints from the literature. Our discussion leads us to address the timing of subduction initiation, the existence of hypothetical ocean basins, the number of intervening subduction zones between the Taurides and the Pontides, the palaeogeographic origin of tectonic units and the possibility for slab break-off during either the Campanian or the Early Eocene. Thence, we put forward a favoured tectonic scenario featuring two successive phases of subduction of a single lithospheric slab and episodic accretion of two continental domains separated by a continental trough, representing the eastern end of the Cycladic Ocean of the Aegean. The lack of univocal evidence for slab break-off in western Anatolia and southward-younging HP/LT metamorphism in continental tectonic units (from ~85, 70 to 50 Ma) in the Late Cretaceous–Palaeogene period suggests continuous subduction since ~110 Ma, marked by roll-back episodes in the Palaeocene and the Oligo-Miocene, and slab tearing below western Anatolia during the Miocene