Hydrogeochemistry of granitic mountain zones and the influence of adjacent sedimentary basins at their tectonic borders:
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PAPER
Hydrogeochemistry of granitic mountain zones and the influence of adjacent sedimentary basins at their tectonic borders: the case of the Spanish Central System batholith Miguel Martín-Loeches 1 & Javier Pavón-García 2 & Eugenio Molina-Navarro 1 & Pedro Martínez-Santos 3 & Carlos Almeida 4 & Jaime Reyes-López 5 & Ignacio Cienfuegos-Hevia 6 & Antonio Sastre-Merlín 1 Received: 6 November 2019 / Accepted: 13 June 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The hydrogeochemical characteristics of springs in the granites of the Spanish Central System (SCS), a mountain range affected by cortical tectonic structures, is described, along with an investigation of the spring water origin. In springs with variable flow and where they are associated with minor alterations and fractures, water type is Ca-(Na)-HCO3 with low total dissolved solids (TDS; 54–200 ppm) and a neutral or slightly acid pH. In springs that have continuous flow and association with relevant fractures, water type is Na-HCO3, with higher pH and TDS (240–563 ppm). There are five springs with water type Na-(Ca)Cl and high TDS (780–9,205 ppm) near the SCS’s southern tectonic borders. Within 5,000 years of apparent residence time, Ca-(Na)-HCO3 water progresses to Na-HCO3 type, slightly increasing HCO3 content, losing Ca due to calcite precipitation and ionic exchange, and gaining S due to sulphate reduction. No changes are observed after 20,000 years of apparent age. The influence of internal CO2 is compatible with Na-HCO3 water type characteristics, facilitated by fracturing. Most of the springs yield cold water; thus, a flow depth up to 500 m can be deduced. Only the Messejana-Plasencia fault region shows Na-HCO3type thermal springs. Chloride type water is a result of the influence of the Tertiary basins’ water moving towards the southern border of the SCS. The reverse fault in such contact, together with the subvertical structures affected by it, are responsible for the springs emerging in the granite. The northern border of the SCS shows the opposite behaviour. Keywords Hydrochemistry . Igneous rocks . Chloride . Groundwater monitoring . Spain Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10040-020-02202-1) contains supplementary material, which is available to authorized users. * Miguel Martín-Loeches [email protected] 1
Department of Geology, Geography and Environment. Geology UD, University of Alcalá, Alcalá de Henares, Madrid, Spain
2
Department of Life Sciences, Botany UD, University of Alcalá, Alcalá de Henares, Madrid, Spain
3
Department of Geodynamic, Stratigraphy and Paleontology, Faculty of Geology, Complutense University of Madrid, C/José Antonio Novais 12, 28040 Madrid, Spain
4
Department of Geology, Universidade de Lisboa, Lisbon, Portugal
5
Instituto de Ingeniería, Universidad Autónoma de Baja California, Boulevard Benito Juárez y Calle de La Normal S/N, Insurgentes Este, 21280 Mexicali, Baja California, Mexico
6
Dirección de Ingeniería. Dpto.
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