Investigation of hydrogeochemical characteristics and quality of the water resources in Şiran (Gümüşhane) district center, Turkey

İnceleme alanı, Gümüşhane (KD Türkiye) ilinin güneybatısında yer alan Şiran ilçe merkezini kapsamaktadır. Bu çalışmada, ilçe merkezindeki suların hidrojeokimyasal karakteristikleri incelenmiş ve metal element içerikleri belirlenmiştir. İnceleme alanında, temel birimleri kumtaşı, kiltaşı, marn, şeyl ve tüf ardışımından meydana gelen Eosen yaşlı Kelkit Formasyonu oluşturmakta olup Kuvaterner yaşlı alüvyon ile uyumsuz bir şekilde örtülmüştür. Bu birimler hidrojeolojik özelliklerine göre taneli gözenekli serbest akiferleri oluşturmaktadır. Örneklerin pH, özgül elektriksel iletkenlik (ÖEİ) ve toplam sertlik (Fr°) değerleri sırasıyla 5.41-7.48, 106.9-141.3 μS/cm ve 4.72-6.78 (n= 18) arasında değişmektedir. Bu veriler, Kıta İçi Yerüstü Su Kaynakları sınıflamasına göre, suların çoğunlukla I. ve II. sınıf, az oranda ise III. sınıf kalitede olduğunu göstermektedir. İnceleme alanındaki sular genelde Ca-Mg-HCO3 tipli karbonatlı (Ca+Mg>Na+K) olup, zayıf asit kökleri güçlü asit köklerinden (HCO3>SO4+Cl) daha fazladır. İnceleme alanındaki suların (Ca+Mg)/(SO4+HCO3) oranları sularda silikat ayrışmasının etkisini işaret etmekte, Cl/(Cl+HCO3) ve (Na+K)/(Na+K+Ca) oranları ise, bu suların kimyasının kayaç yapıcı minerallerin kimyasal ayrışması tarafından kontrol edildiğini, dolayısıyla su-kayaç etkileşimini göstermektedir. Su örneklerindeki çözünmüş potansiyel toksik element içerikleri, birkaç örnek dışında, kabul edilebilir sınırlar arasında dağılım sergilemektedir. Sonuç olarak, elde edilen hidrojeokimyasal veriler, inceleme alanındaki suların genel olarak içme suyu açısından iyi sınıf sular kategorisinde yer aldığını göstermiştir.The study area is located of Şiran District Center in the southwest of Gümüşhane (NE Turkey). In this study, hydrogeochemical characteristics of water resources in district center were examined and metal element contents were determined. In the study area, the basement rocks are represented by Eocene Kelkit formation, which is composed of sandstone, claystone, marl, shale and tuff, and this unit is covered unconformably by the Quaternary aged alluvium. These units form granular porous unconfined aquifers according to the hydrogeological features. The pH, specific conductance (SC) and hardness (Fr°) values of the water resources in the study area varied between 5.41-7.48, 106.9-141.3 µS/cm and 4.72-6.78 (n= 18), respectively. According to the classification of Intra-Continental Water Resources, these data show that the samples are mostly class-I and II, rarely class-III water quality characteristics. The water resources in the study area are generally classified as Ca-Mg-HCO3 type carbonated (Ca+Mg>Na+K), and generally their weak acids are more than strong acids (HCO3>SO4+Cl). In the study area, (Ca+Mg)/(SO4+HCO3) ratios indicated the effect of silicate weathering in the waters, and the Cl/(Cl+HCO3) and (Na+K)/(Na+K+Ca) ratios show that the chemistry of waters is controlled by the chemical weathering of rock-forming minerals, hence, reflect the water-rock interaction. Except for a few, the concentration of dissolved potentially toxic elements in the water samples were distributed within acceptable limits. Consequently, the hydrogeochemical results showed that the water resources in the study area were in the category of good class waters in terms of drinking water

Petrogenesis of post-collisional Middle Eocene volcanism in the Eastern Pontides (NE, Turkey): Insights from geochemistry, whole-rock Sr-Nd-Pb isotopes, zircon U-Pb and 40Ar-39Ar geochronology

International audienceThe debate about whether Eocene magmatism is considered to be post-collisional or subduction-related or not still continues. Here we offer new 40Ar-39Ar ad U-Pb zircon geochronology, mineral chemistry, bulk rock and Sr-Nd-Pb isotope geochemistry data obtained from the southern dike (SD) suite, in comparison with the northern dike (ND) suite, from the Eastern Pontides. The geochronological data indicate that the SD suite erupted between 45.89 and 45.10 Ma corresponding to the Lutetian (Middle Eocene). The magmas of the ND suite are characterised by slightly more alkaline affinity compared to the SD suite. The trace and rare earth element (REEs) content of the SD suite is characterised by large ion lithophile element (LILEs; Sr, K2O, Ba, Rb) enrichment and depletion of Nb, Ta, and TiO2 elements to different degree with high Th/Yb ratios, which indicate that the magmas forming the SD and ND suites were derived from lithospheric mantle sources enriched by mostly slab-derived fluids in the spinel stability field. The Sr, Nd and Pb radiogenic isotope ratios of the dikes support the view that the magma for the hydrous group (H-SD) was derived from a relatively more enriched mantle source than the other SD and ND suites. The ND suite and the anhydrous group (A-SD) display similar geochemical features characterised by moderate light earth element (LREE)/heavy rare earth element (HREE) ratios, while the H-SD group has respectively lower LREE/HREE ratios indicating higher melting degree. Detailed considerations of the alkalinity, enrichment and partial melting degree for the source of the studied volcanic rocks indicate that the magmas of the northern dike suite are characterised by slightly more alkaline affinity, whereas the magmas throughout the southern dike suite show increments in the enrichment rate and melting degree. In light of the obtained data and comparative interpretations, the geodynamic evolution and differences in petrogenetic character of the Lutetian magmas from both the northern and southern parts of the Eastern Pontides may be explained by different degrees of melting of a net veined mantle source initially metasomatized by mostly subduction fluids during asthenospheric upwelling due to fragmented asymmetric delamination in a post-collisional extensional tectonic environment

40Ar–39 Ar dating, whole-rock and Sr-Nd isotope geochemistry of the Middle Eocene calc-alkaline volcanic rocks in the Bayburt area, Eastern Pontides (NE Turkey): Implications for magma evolution in an extension-related setting

International audienceDiscussions continue about whether Middle Eocene magmatism in the Eastern Pontides is associated with collision or subduction. This paper presents new whole-rock geochemistry, Sr-Nd isotopic and 40Ar-39Ar age data for Middle Eocene volcanic rocks from the Bayburt area of the Eastern Pontides (NE Turkey) to investigate their sources and evolutionary history. The new 40Ar–39Ar ages reveal that these volcanic rocks erupted between 44.6 ± 0.1 Ma and 43.5 ± 0.1 Ma, within the Lutetian (Middle Eocene). The studied volcanic rocks are composed of basalt, andesite, basaltic andesite and minor dacite lava and pyroclastic rocks. These rocks consist of plagioclase, amphibole, pyroxene, olivine, biotite, sanidine and minor quartz phenocrysts with Fe-Ti oxides. They have microlithic, hyalo-microlithic, porphyritic and rarely glomeroporphyritic textures. The volcanic rocks have low to high-K calc-alkaline affinities. They display enrichment in large-ion lithophile elements and depletion in high-field strength elements with high Th/Yb ratios, which indicate that the magmas forming the volcanic rocks were derived from lithospheric mantle sources enriched by mostly slab-derived fluids in the spinel stability field. 87Sr/86Sr(i) values vary between 0.70485 and 0.70551 and 143Nd/144Nd(i) values vary between 0.51255 and 0.51267. These data correspond to the mantle array on the isotope ratio diagram. The main solidification processes consist of fractional crystallization with minor assimilation. In light of the data obtained in this study together with data from previous studies, petrogenetic character of the Middle Eocene magmas from the southern parts of the Eastern Pontides may be explained by melting of an enriched lithospheric mantle source initially metasomatized by subduction fluids in a post-collisional extensional-related tectonic setting

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