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Using a portable gas analyzer system, the geogenic gas regime below and around an ancient gate to hell at Hierapolis/Phrygia was characterized. The site was first described by Strabo and Plinius as a gate to the underworld. During centuries, it attracted even ancient tourists. In a grotto below the temple of Pluto, CO2 was found to be at deadly concentrations of up to 91%. Astonishingly, these vapors are still emitted in concentrations that nowadays kill insects, birds, and mammals. The concentrations of CO2 escaping from the mouth of the grotto to the outside atmosphere are still in the range of 4-53% CO2 depending on the height above ground level. They reach concentrations during the night that would easily kill even a human being within a minute. These emissions are thought to reflect the Hadean breath and/or the breath of the hellhound Kerberos guarding the entrance to hell. The origin of the geogenic CO2 is the still active seismic structure that crosses the old town of ancient Hierapolis as part of the Babadag fracture zone. Our measurements confirm the presence of geogenic CO2 in concentrations that explain ancient stories of killed bulls, rams, and songbirds during religious ceremonies. They also strongly corroborate that at least in the case of Hierapolis, ancient writers like Strabo or Plinius described a mystic phenomenon very exactly without much exaggeration. Two thousand years ago, only supernatural forces could explain these phenomena from Hadean depths whereas nowadays, modern techniques hint to the well-known phenomenon of geogenic CO2 degassing having mantle components with relatively higher helium and radon concentrations. C1 [Pfanz, Hardy] Univ Duisburg Essen, Inst Appl Bot & Volcano Biol, D-45117 Essen, Germany. [Yuece, Galip] Hacettepe Univ, Dept Geol Engn, TR-06800 Ankara, Turkey. [Gulbay, Ahmet H.] Eskisehir Osmangazi Univ, Dept Geol Engn, TR-26480 Meselik, Eskisehir, Turkey. [Gokgoz, Ali] Pamukkale Univ, Dept Geol Engn, Denizli, Turkey.

We investigated the geochemical features of the fluids circulating over the Amik Basin (SE Turkey–Syria border), which is crossed by the Northern extension of the DSF (Dead Sea Fault) and represents the boundary area of three tectonic plates (Anatolian, Arabian and African plates). We collected 34 water samples (thermal and cold from natural springs and boreholes) as well as 8 gas samples (bubbling and gas seepage) besides the gases dissolved in the sampled waters. The results show that the dissolved gas phase is a mixture of shallow (atmospheric) and deep components either of mantle and crustal origin. Coherently the sampled waters are variable mixtures of shallow and deep ground waters, the latter being characterised by higher salinity and longer residence times. The deep groundwaters (from boreholes deeper than 1000 m) have a CH 4 -dominated dissolved gas phase related to the presence of hydrocarbon reservoirs. The very unique tectonic setting of the area includes the presence of an ophiolitic block outcropping in the westernmost area on the African Plate, as well as basalts located to the North and East on the Arabic Plate. The diffuse presence of CO 2 -enriched gases, although diluted by the huge groundwater circulation, testifies a regional degassing activity. Fluids circulating over the ophiolitic block are marked by H 2 -dominated gases with abiogenic methane and high-pH waters. The measured 3 He/ 4 He isotopic ratios display contributions from both crustal and mantle-derived sources over both sides of the DSF. Although the serpentinization process is generally independent from mantle-type contribution, the recorded helium isotopic ratios highlight variable contents of mantle-derived fluids. Due to the absence of recent volcanism over the western side of the basin (African Plate), we argue that CO 2 -rich volatiles carrying mantle-type helium and enriched in heavy carbon, are degassed by deep-rooted regional faults rather than from volcanic sources.