1. The Campo de Calatrava Volcanic Field (central Spain): Fluid geochemistry in a CO2-rich area
- Author
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Nisi B.[1], Vaselli O.[1, Elio J.[4], Giannini L.[2, Tassi F.[2, Guidi M.[1], Darrah T.[5], Maletic E., Delgado Huertas A.[6], and Marchionni S.[2]
- Subjects
geography ,geography.geographical_feature_category ,Evaporite ,Geochemistry ,Aquifer ,010501 environmental sciences ,010502 geochemistry & geophysics ,01 natural sciences ,Pollution ,Mg-HCO3 waters ,Volcanic rock ,Isotopic signature ,Basement (geology) ,Volcano ,Campo de Calatrava volcanic field ,Geochemistry and Petrology ,Central southern Spain ,Geopressurized CO2-Rich reservoir ,Fluid geochemistry ,Environmental Chemistry ,Sedimentary rock ,Quaternary ,Geology ,0105 earth and related environmental sciences - Abstract
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 CO emitting zones in Peninsular Spain. Here, we report and evaluate new molecular and isotopic geochemistry of thermal waters and COrich gas discharges from the CCVF. Locally, these CO-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) HCO-Mg(Ca) type waters, associated with a relatively shallow aquifer and related to the interaction of meteoric waters with CO-rich gases, alkaline volcanic products, and sedimentary formations, 2) SO(Cl)-Ca(Mg) type waters, which stems from the two rivers (Guadiana and Jabalón) that drain Triassic evaporitic rocks before entering the study area, and 3) HCO-Na type waters, hosted in deep geopressurized CO-rich reservoirs within the Ordovician basement rocks. The Sr/Sr isotopic compositions (ranging between 0.70415 and 0.71623) and δS-SO values (+10.7 to +18.3‰ vs. CDT) of CO-rich fluids are consistent with interactions between water and either the Paleozoic basement, Triassic evaporites, Quaternary volcanic rocks, or a combination thereof. Dissolution of a CO-rich gas phase into the aquifer produces low pH values (down to 5.4) and enhances water-rock interactions causing relatively high salinity (Total Ionic Salinity: up to ∼185 meq/L). Carbon dioxide is by far the most abundant gas constituent (up to 992 mmol/mol) and is dominated by mantle-derived sources as indicated by the combination of relatively high helium isotopic ratios (up to 2.7 R/Ra), high isotopic ratios of carbon in CO (ranging between −6.8 and −3.2‰ V-PDB), and the carbon isotopic signature of TDIC (from −6.8 to +2.2‰ vs. VPDB). In the last two decades, numerous (CO-rich) gas blowouts have occurred in the area during well drillings, suggesting the presence of a geopressurized gas reservoir at relatively shallow depth., The Municipality of Almagro is gratefully acknowledged for the help provided during the sampling activities. We would like to thank Dr. Luis Perez del Villar for his help during the first sampling fieldwork at CCVF. We wish to thank D. Melero Cabañas who accompanied us in the field to collect the water samples during the first survey. Many thanks are also due to the personnel of Amphos21 (J. Bruno, A. Cedez, F. Grandia) and Ciudad de la Energia (D. Angel) and F. Capecchiacci (Dept. Earth Science of Florence) for their help during the second survey. We would like to acknowledge the comments and suggestions provided by two reviewers, who greatly improved an early version of the manuscript. This work was partially funded by Ciudad de la Energia (Resp. OV; Grant contract: ALM-08-006) and the Laboratory of Stable Isotopes and Fluid Geochemistry of the Department of Earth Sciences (University of Florence).
- Published
- 2019
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