The Campo de Calatrava Volcanic Field (central Spain): Fluid geochemistry in a CO2-rich area

摘要

The Campo de Calatrava Volcanic Field (CCVF) located in central-southern Spain (along with Selva-Emporda in Catalonia, NE Spain) is regarded as one of the most important CO2 emitting zones in Peninsular Spain. Here, we report and evaluate new molecular and isotopic geochemistry of thermal waters and CO2 rich gas discharges from the CCVF. Locally, these CO2 -rich fluid emissions represent the remnants of the past volcanic activity that affected this area from the late Miocene through the Quaternary, with the most recent events occurring in the Holocene. The locations of discharging fluids and previous volcanic centers appear to be aligned along well-defined NW-SE and NNW-SSE lineaments, with subordinate trends in the ENE-WSW direction. The chemical and isotopic composition of the thermal waters suggests a meteoric origin, dominated by three distinct geochemical facies: 1) HCO3-Mg(Ca) type waters, associated with a relatively shallow aquifer and related to the interaction of meteoric waters with CO2-rich gases, alkaline volcanic products, and sedimentary formations, 2) SO4(Cl)-Ca(Mg) type waters, which stems from the two rivers (Guadiana and Jabalon) that drain Triassic evaporitic rocks before entering the study area, and 3) HCO3-Na type waters, hosted in deep geopressurized CO2-rich reservoirs within the Ordovician basement rocks.