Quantification of the Mixture of Hydrothermal and Fresh Water in Tectonic Valleys
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ISSN 1674-487X
Quantification of the Mixture of Hydrothermal and Fresh Water in Tectonic Valleys Janete Moran-Ramírez
1
, José Iván Morales-Arredondo *2, Maria Aurora Armienta-Hernández2, José Alfredo Ramos-Leal3
1. National Council of Science and Technology, National Autonomous University of Mexico, Institute of Geophysics, Scientific Research Circuit, University City, Coyoacán 04150, Mexico City, Mexico 2. National Autonomous University of Mexico, Institute of Geophysics, University Campus, Mexico City, Mexico 3. Potosino Institute for Scientific and Technological Research, 78216 San Luis Potosí, S. L. P., Mexico Janete Moran-Ramírez: https://orcid.org/0000-0002-3209-0069; José Iván Morales-Arredondo: https://orcid.org/0000-0002-7529-992X ABSTRACT: This study was conducted to identify the origin, hydrogeochemical processes and evolution of groundwater in a tectonic valley. This study was carried out with the aim of quantifying the proportions of groundwater flows contributing to the water chemistry abstracted in a zone of convergence favored by the presence of active faults. The study area is located in the Trans-Mexican Volcanic Belt. End members methodology was applied to identify the mixing of hydrothermal with fresh groundwater, where changes in the aquifer geology result in distinct groundwater chemical signatures. Ternary mixing was quantified using conservative elements. Moreover, other evolutionary processes, such as ion exchange and silicate weathering occur due to changes in the geology of the area. In ternary mixing, each of the end members is associated with the lithology through which it circulates. The local flow contributes 70% of the water to the system, the intermediate flow contributes 14%, and the regional flow contributes 16%. Three types of water are produced: Na-HCO3, due to the interaction of water with volcanic rocks of rhyolitic composition, Na-Mg-HCO3, due to the interaction of water with volcanic rocks of basaltic-andesite composition, and Ca-HCO3, due to the interaction of water with sedimentary calcareous rocks. KEY WORDS: hydrogeochemistry, ternary mixing, end members, conservative elements, local flow, Mexico. 0
INTRODUCTION Volcano-sedimentary aquifers in tectonic valleys are complex due to the interdigitation of sedimentary and volcanic materials as well as the presence of faults. The hydraulic conductivity is influenced by this heterogeneity; moreover, the infiltration rates through fractures may be extremely high (Cook et al., 2003). In general, these changes in geological conditions are reflected in the chemical characteristics of groundwater. Different studies have been investigated to understand these processes in tectonic valleys, some with the presence of active faults. These hydrogeochemical processes facilitate the mixing of thermal and cold groundwaters, as reported in a study to identify geothermal fields in the Xinzhou Basin, Shanxi Province, China (Han et al., 2010). Hydrogeochemical studies allowed to define the mixing processes of water with distinct temperatures
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