Bulk-rock major, trace, and REE geochemistry and Pb-Sr-Nd isotopic compositions identify mantle sources involved in the genesis of volcanic rocks of the Upper Cretaceous-Lower Tertiary Ulukişla Formation, Çamard-Ulukişla Basin, Nigde Province, central Anatolia. Incompatible trace-element patterns exhibit a large Nb-Ta trough and strong enrichment of LILE such as Ba, Th and U, and LREE, which indicate a subduction-zone signature. Trace-element ratios are compatible with a subcontinental lithospheric source. Isotopic data demonstrate the presence of an EMII-like protolith (87Sr/86Sr = 0.707242-0.707582, 143Nd/144Nd = 0.512336-0.512390, 206Pb/204Pb = 18.70-18.917, 207Pb/204Pb = 15.716-15.796, 208Pb/204Pb = 39.157-39.45). These geochemical and isotopic data indicate the derivation of the studied volcanic rocks from an enriched subcontinental mantle source, modified by earlier subduction events. This petrogenetic conclusion is compatible with a geodynamic setting of post-collisional extension for the Çamard-Ul...

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 δ¹³C_CO2 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.

Mainly calc-alkaline, andesitic, and dacitic volcanics from different late Miocene-Pliocene eruption centers crop out WSW of Konya, and locally are interbedded with lacustrine sediments. Hydrothermal alteration within these rocks is widespread. In addition to kaolinite, other major alteration products include halloysite, alunite, cristobalite, quartz, illite, montmorillonite, and zeolitegroup minerals. Based on the cristobalite-quartz relationship, the kaolinization temperature is estimated as ∼100°C. The samples were mineralogically and chemically examined using XRD, SEM-EDS, IR, DTA-TG, and XRF. The crystallinity of the kaolinite is moderate, and shows structural disorder. Both the kaolinite and halloysite are almost stoichometric. Kaolinization generally led to Al₂O₃ increases and release of alkalies, alkaline earths, most of the Fe₂O₃, and SiO₂. SiO₂ and Al₂O₃ contents are low, and LOI is very high for halloysite deposits relative to kaolin occurrences. The kaolinite-alunite assemblages indicate that pH of the altering solutions initially was ∼4. SEM investigation demonstrates that kaolinite has booklet texture, whereas halloysite is acicular to needleshaped. The chemical, mineralogic, and firing properties of the kaolin deposits are appropriate for use as refractory raw material. The Erenler Dagi kaolin deposits are excellent examples of the acid-sulfate type of hydrothermal alteration. The findings of the study may be useful in exploration for similar hydrothermal mineral occurrences worldwide.

Most of the nitrogen (N) accessible for life is trapped in dinitrogen (N ₂ ), the most stable atmospheric molecule. In order to be metabolized by living organisms, N ₂ has to be converted into biologically assimilable forms, so-called fixed N. Nowadays, nearly all the N-fixation is achieved through biological and anthropogenic processes. However, in early prebiotic environments of the Earth, N-fixation must have occurred via natural abiotic processes. One of the most invoked processes is electrical discharges, including from thunderstorms and lightning associated with volcanic eruptions. Despite the frequent occurrence of volcanic lightning during explosive eruptions and convincing laboratory experimentation, no evidence of substantial N-fixation has been found in any geological archive. Here, we report on the discovery of a significant amount of nitrate in volcanic deposits from Neogene caldera-forming eruptions, which are well correlated with the concentrations of species directly emitted by volcanoes (sulfur, chlorine). The multi-isotopic composition (δ ¹⁸ O, Δ ¹⁷ O) of the nitrates reveals that they originate from the atmospheric oxidation of nitrogen oxides formed by volcanic lightning. According to these first geological volcanic nitrate archive, we estimate that, on average, about 60 Tg of N can be fixed during a large explosive event. Our findings hint at a unique role potentially played by subaerial explosive eruptions in supplying essential ingredients for the emergence of life on Earth.