Thermal springs in Northern Tunisia: geochemical study and their relation with tectonic features

摘要

About twenty hot springs in northern Tunisia have been investigated and compared with six complex geothermal cold springs. The main aim of this study is to access the role of geologic structure and litliostratigraphic sequence in the emergence, behaviour and the physical as well as chemical composition of these hydrothermal systems. The spring waters analysed present an isotopic composition in I8O and 2H that suggest a meteoric origin with no meaningful enrichment in 18O due to the high temperature. Besides, values of the tritium and HC show that the Tunisian hot-springs result from the mixing of old waters poor in Tritium with younger waters with higher Tritium-content. The study of the interactions between the rocks and the waters confirms the existence of a partial state of equilibrium with regards to rocks of average crustal composition. The majority of the waters flow along lengthy deep-rooted fault plains before emerging in the Mesozoic carbonate and evaporitic aquifers. These hydrothermal activities are related to other profound activities as confirmed by the distribution of the partial CO2 (PcO2) pressure in the waters.