Geochemistry of fluid inclusions in travertines from Western and Northern Turkey: inferences on the role of active faults in fluids circulation

The understanding of the relationship between the geochemistry of fluids circulating during travertine deposition and the presence of active faults is crucial for evaluating the seismogenetic potential of an area. Here we investigate travertines from Pamukkale and Reşadiye (Turkey), sited in seismic regions and next to thermal springs. These travertines formed ~24,500–50,000 (Pamukkale) and ~240–14,600 years (Reşadiye) BP. We characterize fluid inclusions (FIs) and studied concentration of H2O, CO2, O2 + N2, and 3He, 4He, 20Ne, and 40Ar, and bulk composition (trace elements and δ13C‐δ18O). FIs from both localities are mainly primary with low salinity and homogenization temperature around 136–140 °C. H2O is the major component followed by CO2, with the highest gas content measured in Pamukkale travertines. Concentrations of Ne‐Ar together with O2 + N2 indicate that travertines from both areas precipitated from atmosphere‐derived fluids. The 3He/4He is 0.5–1.3 Ra in Pamukkale and 0.9–4.4 Ra in Reşadiye. Samples with R/Ra > 1 are modified by cosmogenic 3He addition during exposure to cosmic rays. Excluding these data, FIs of Reşadiye are mostly atmosphere‐derived. This implies a shallow formation where the circulation was dominated by meteoric waters, which is consistent with their young age. Instead, FIs of Pamukkale show mixing of mantle‐, crustal‐, and atmosphere‐derived He, indicating that these travertines formed in lithospheric fractures. Based on the δ13CCO2 and δ18O of bulk rocks, we infer that travertines formed involving crustal‐ (mechanochemical rather than organic) and mantle‐derived CO2. Trace elements of Pamukkale and Reşadiye show comparable rare earth element patterns. We conclude that travertines formed in response of seismogenetic activity.Published5473-54982T. Deformazione crostale attiva7T. Variazioni delle caratteristiche crostali e precursori sismici6A. Geochimica per l'ambiente e geologia medicaJCR Journa

Textural and compositional evidence for magma mixing in the evolution of the Camhdere volcanic rocks (Galatean Volcanic Province), Central Anatolia, Turkey

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Mineralogical and geochemical characteristics and genesis of the sepiolite deposits at Polatli Basin (Ankara, Turkey)

The Middle-Upper MiocenePliocene sediments near Polatli{dotless} contain commercial sepiolitic clay deposits. The sepiolite-rich Polatli{dotless} basin sediments were studied to describe the sepiolitic clay deposits of the area and to assess the environments of formation using X-ray diffraction, optical and scanning electron microscopy, and chemical analysis. The Polatli{dotless} basin is an elongated, rift-related graben trending NESW in central Turkey, filled with continental Late Miocene to Early Pliocene sediments. The sediments which comprise claystone, marl and limestone, dolostone, and evaporites are characteristic deposits of low-salinity, playa-lake depositional environments. These sepiolite-rich deposits include sepiolite, dolomite, and calcite, with minor amounts of palygorskite, quartz, moganite, amorphous silica (opal-CT), and feldspar. The sepiolite shows all the characteristic X-ray diffraction reflections of that mineral, whereas amorphous silica containing sepiolite shows some of the characteristic reflections of sepiolite, but with somewhat broader and less intense basal reflections. In the siliceous deposits, the long, fibrous, and filamentous aggregates of the sepiolite were converted to thick, short fibers, low in Mg, and showing transition to amorphous silica. Major and trace elements (e.g. Si, Al, Fe, Mg, Sr, Ba, etc.) were found almost exclusively in Mg-rich smectitic claystone and detrital silicate-rich rocks, whereas Mg, Ca, and some Si were concentrated in the neoformed minerals in the basin. The rare-earth elements (REE) and some of the high-field strength elements (HFSE), large ion lithophile elements (LILE), and transition elements (TRE) patterns were similar for detrital silicate-rich rocks and formed from neoformed mineral lithologies. The REE, TRE, LILE, and some of the HFSE contents of limestone, dolostone, and sepiolitic claystone were similar while those of detrital silicate-rich rocks and Mg-rich smectitic claystones were similar to each other. PAASnormalized REE and other trace-element patterns were typically subparallel and depleted in neoformed minerals. All sample groups had positive Eu* anomalies, except Mg-rich smectite (0.80). Limestone, dolostone, and amorphous silica compounds showed slightly negative Ce* anomalies, whereas sepiolitic claystones, Mg-rich smectitic claystones, and detrital silicate-rich rocks had a slightly positive Ce* anomaly

Early Miocene adakite-like volcanism in the Balkuyumcu region, central Anatolia, Turkey: Petrology and geochemistry

International audienceThe Balkuyumcu region, located in the southwestern part of Ankara in the Izmir-Ankara suture zone (central Anatolia, Turkey), consists of basic andesitic, andesitic, dacitic and rhyolitic rocks extruded during the Early Miocene (20–22 Ma) as a result of post-collisional volcanism. Balkuyumcu volcanic rocks can be divided into two groups on the basis of their mineralogy and composition: The basic andesitic (BA) and andesitic, dacitic and rhyolitic (ADR) groups. The ADR and BA group of rocks have adakite-like and calc-alkaline characteristics, respectively. The ADR group has higher SiO2 content, Sr/Y and La/Yb ratios and low MgO, Mg#, Y and Yb contents than the BA group. Both groups have nearly the same Sr, Nd isotopic compositions and display similar normalized multi-element patterns with enrichments in LILE and LREE, depletions in Nb, Ti, Zr, P and a lack of Eu anomalies. Major, trace element and Sr, Nd isotopic data indicate that both groups of rocks were derived from the same source but affected by different magmatic processes during ascent. The adakite-like rocks may have been produced by partial melting of thickened lower continental crust. Fractional crystallization also played a major role in their formation. However, the BA group rocks were derived from partial melting of lower continental crust that was probably delaminated. These rocks appear to have had limited interaction with mantle peridodite during ascent to the surface

Petrogenesis of the Neogene bimodal magmatism of the Galatean Volcanic Province, Central Anatolia, Turkey

International audienceA series of geochemical analyses and radiometric age determinations are undertaken on rock samples collected from the Çamlıdere region in the Galatean Volcanic Province of NW Turkey, to better understand the characteristics of the bimodal Early-Middle Miocene volcanism developed near the Late Cretaceous Tethyan Suture Zone. Çamlıdere volcanic rocks consist of large volumes of older (> 20 Ma) calc-alkaline andesites, dacites and rhyolites and pyroclastites, and small volumes of slightly younger (~ 19 Ma) alkaline trachybasalts and basaltic trachyandesites, cropping out as dykes or small lava flows. The older rocks exhibit elevated LILE, LREE and depleted HFSE contents, carrying geochemical characteristics suggesting earlier subduction process. Some samples of the younger mildly alkaline lavas display geochemical characteristics of intraplate magmatism with enrichment of LILE contents with little or no HFSE depletion. Knowing that the Galatean volcanic rocks experienced syn-volcanic extensional tectonics during the Miocene, we think that the reactivation of the old suture zone produced first calc-alkaline series originated from a subduction-modified subcontinental lithospheric mantle, followed by more alkaline products. However, some volcanic rocks suggest penetration of small amounts of asthenospheric melts to this lithospheric mantle source. The regionally known last volcanic phase produced small amounts of alkaline basaltic rocks in Güvem area at about 10 Ma. Volcanic activities ended possibly with, or just after the Güvem event, when the extensional tectonic regime switched to strike-slip faulting in the region, with the inception of one of the major faults of Turkey, the North Anatolian Fault Zone

Complex remanent magnetization in the Kızılkaya ignimbrite (central Anatolia): Implication for paleomagnetic directions

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Magnetic fabric of ignimbrites: a case study from the Central Anatolian Volcanic Province

International audienceThe magnetic fabric of the Pliocene Kızılkaya ignimbrite in the Central Anatolian Volcanic Province has been investigated by anisotropy of magnetic susceptibility (AMS) and isothermal remanent magnetization (AIRM). Seven sections were sampled at various stratigraphic heightswithin the devitrified portion of the ignimbrite. The magnetic mineralogy is complex: titanomagnetite occurs as magmatic grains, and as inclusions in other phenocryst and glass shards; an oxidized phase and hematite occur in deposit levels affected by alteration processes. The disturbanceproduced by lithic and pumice clasts has been reduced by discarding the specimens that deviate more than +1s from the site mean value of the density. The AMS fabric varies along each individual section. Neither the AMS magnetic lineation nor the magnetic foliation plungeclearly define a common area as the vent location. The AIRM fabric of low-coercivity minerals, mainly represented by free titanomagnetite grains of magmatic origin, is consistent between sites and the inferred flow directions converge on a region near Derinkuyu, in the Nevsehirplateau, previously reported as the Kızılkaya ignimbrite source area. This study shows that systematic use of the remanent fabric improves the results given by AMS and aids th