Origin and interactions of fluids circulating over the Amik Basin (Hatay, Turkey) and relationships with the hydrologic, geologic and tectonic settings

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 theDSF (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 (fromboreholes deeper than 1000 m)have a CH4-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 CO2-enriched gases, although diluted by the huge groundwater circulation, testifies a regional
degassing activity. Fluids circulating over the ophiolitic block are marked by H2-dominated gases with
abiogenic methane and high-pH waters. The measured 3He/4He 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 CO2-rich volatiles carrying mantle-type helium and enriched in heavy carbon, are degassed
by deep-rooted regional faults rather than from volcanic sources.