Thermal Water's Isotope Geochemistry Study of Evros Area, NE Greece

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IOP Conference Series: Earth and Environmental Science PAPER OPEN ACCESS Thermal Water's Isotope Geochemistry Study of Evros Area, NE Greece To cite this article: Dotsika Elissavet and Chantzi

1 IOP Conference Series: Earth and Environmental Science PAPER OPEN ACCESS Thermal Water's Isotope Geochemistry Study of Evros Area, NE Greece To cite this article: Dotsika Elissavet and Chantzi Paraskevi 2016 IOP Conf. Ser.: Earth Environ. Sci View the article online for updates and enhancements. This content was downloaded from IP address on 25/07/2018 at 16:07

2 Thermal Water's Isotope Geochemistry Study of Evros Area, NE Greece Dotsika Elissavet 1,2, Chantzi Paraskevi 1 1 Laboratory of Stable Isotopes and Radiocarbon, Institute of Nanoscience & Nanotechnology, NCSR Demokritos, , Greece 2 Institute of Geosciences and Earth Resources, Via G. Moruzzi 1, Pisa, Italy e.dotsika@inn.demokritos.gr Abstract. Thermal waters from Evros area were collected and subjected to chemical and isotopic analysis in order to understand all the physicochemical mechanisms (mixing, dilution, precipitating) that contribute to the shallow and deep geothermal water tables and determine the origin of these fluids as well as their mineralization. Physicochemical characteristics EC, T C, ph was determined at the field. The ionic concentrations of samples indicate solutions with high salinity. Two chemical water types were arisen: Na-SO 4 concerning low temperatures and shallow aquifers and Na- Cl concerning high temperatures and deeper geothermal circulation. The ratio Br/Cl definitely considered marine origin indicator is the same as the sea confirming the involvement of the seawater in the geothermal system. The marine component and water-rock interaction process under high temperatures seem to contribute to the mineralization of thermal waters. Moreover, water-rock interaction process is also responsible for the alternation of δ 18 O values. Geothermometers concluded to a middle enthalpy geothermal field. 1. Introduction Tectonic activity, thinning of the cortex, the magmatic intrusions (plutonic and volcanic rocks), the increased circumferential heat flux, large open cracks affecting groundwater and overlap the sedimentary sequences, the existence of impermeable layers can function as "impervious cover" and the presence of aquifers through permeable sediments are favorable conditions for the formation of geothermal fields in sedimentary basins in northeastern Greece. The Tertiary sedimentary basins of Strimona, Nestos, Xanthi, Komotini and Evros Delta in the Rhodope region (Northern Greece) controlled by faults which extend largely in the area. Their orientations vary across the area (Strimona basin is oriented NW-SE, the Nestos Delta - Prinos basin are of NE-SW orientation and Xanthi- Komotini basin is of EW direction). A series of molasses by conglomerates, sandstones, marls and limestones with lignite presence dates from middle Eocene - Oligocene and possibly up to the base of the Miocene and is configured in Xanthi-Komotini basin and Evros Delta (Alexandroupoli). Neogene and Quaternary sediments pay all basins in Eastern Macedonia and Thrace (Northern Greece). Waters were sampled from Strimona, Sidirokastro, Eleftheres, Akropotamos and Agistro as well as a cold water Agistro as a reference sample for cold waters in the northern part of Greece. Then sampling was Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by Ltd 1

3 performed in Erateino, Myrodato and Erasmio stations in delta basin of Nestos and Potamia station in Xanthi-Komotini basin. Finally, a sample was also taken from Thermes station in Xanthi-Komotini basin. 2. Geochemical analysis The positive correlation between Cl - and Na + (Figure 1, left) in thermal waters implies that high concentrations of Cl - (TRA 1, POT-1, MYR, ERA 6, ERT 1, AKR-1) resulting from seawater participation or/and a deep Na-Cl geothermal liquid. However, Cl - and Br - ions (and 2 H) are retained in geothermal environments as their concentration is not affected by interactions with the rock unlike Na + [1-4]. Therefore, the origin of dissolved salts in thermal liquids is investigated using the ratio Cl/Br. In Cl-Br diagram (Figure 1, right) samples were placed on the seawater dissolution line displaying similar behavior and Cl/Br ratios between 259 and 303, close enough to that of seawater 320. The correlation between Cl - and Br - was used in order to determine marine contribution in samples assuming that this contribution originates by a marine component. The two equations are listed in Table 1 presenting similar results. Figure 1. Left: Na + vs Cl - diagram and Right: Br - vs Cl - diagram of thermal waters in Eastern Macedonia and Thrace [*: sampling stations; + seawater, : seawater dissolution line] Table 1. Seawater contributions (%) in selected thermal waters calculated from the mass equation of Cl - and Br - concentrations. Sampling station mixing with sea water mixing with sea water % % (Cl - ) (Br - ) TRA POT ERA ERT AKR ELF The Mg/Cl (Figure 2, left) and Ca/Cl (Figure 2, right) ratios that presented in thermal water are lower and higher respectively than that of sea water implying an interaction of the deep water originating from volcanic formations with high temperature and CO 2 pressures. In fact, at high temperatures the Mg 2+ is incorporated in the secondary rocks through water-rock interaction and [5] thus it is removed from the solutions. In Mg/Cl diagram (Figure 2, left) three water types occurred. The first concerns samples from Agistro (AGI-1), Sidirokastro (SID-1), Thermes (THE-1) with Mg/Cl ratio lower than that of seawater suggesting the interaction of deep water originating from volcanic formations with high temperature and CO 2 pressures. The second concerns samples from Neo Erasmio (ERA15, ERA1) with particularly high 2

4 Mg/Cl ratio and the third rest of samples (TRA1, POT1, MDP, ERA6, ELF1, AKR1, ERT1) with moderate high Mg/Cl ratio. Similar behavior exhibits Ca-Cl ratio for the first (AGI-1, SID-1, THE-1) and the second group (ERA15, ERA1). The third group presents a very good correlation with elevated Ca 2+ values for samples TRA1, ERA6, ERT1. These high values Ca 2+ are due to the balance of geothermal minerals (Na-K-quartz, calcite, muscovite) at high temperature (> 200 o C) [6] and CO 2 pressures. Figure 2. Left: Mg 2+ vs Cl - diagram and Right: Mg 2+ vs Cl - diagram of thermal waters in Eastern Macedonia and Thrace [*: sampling stations; + seawater] Figure 3. Left: B + vs Cl - diagram and Right: Cl/B vs Cl - diagram of thermal waters in Eastern Macedonia and Thrace [*: sampling stations; + seawater] In order to highlight the water-rock interaction mechanisms Cl-B diagram was used with main sources for these ions the meteoric water, the water-rock interaction (for B + ) and/or mixing with underground seawater or brines (for Cl - ). The concentration of B + in volcanic rocks presents mean temperatures between 10 and 40ppm [7]. As the dissolution of rocks is in progress the Cl/B ratio in thermal water solution gradually reaches that of rock. Therefore, a significant quantity of B + in geothermal waters comes from water-rock interaction process but only a small amount of Cl -, as rocks do not contain significant quantities Cl - except evaporates. The Cl/B ratio (Figure 3, left) is less than that of seawater in all stations implying the water-rock interaction process. However, a parallel increase of Cl/B ratio and Cl - concentration is observed in the admixture with a Na-Cl geothermal water type or seawater as shown in Figure 3 (right) for TRA1, POT1, MDP, ERA6, ELF1, AKR1 and ERT1 stations. 3

5 3. Isotopic analysis δ 18 O and δ 2 Η of water samples The range of isotopic values for the area of East Macedonia and Thrace was from (AGI-1) to (ERT1) for δ 18 O and from -65,93 (AGI-1) to -41,6 (ERT 1) for δd. The correlation between δ 18 O values and recharge altitude results in an altitude effect about /100m in Macedonia and /100m in Thrace. Mra = (-1026 ± 130) (221± 15) δ 18 O; East Macedonia, [8] (1) Mra = (-2800 ± 115) (459 ± 15) δ 18 O; Thrace, [8]. (2) According to this model AGI1 and SID1 stations should correspond to 1180m and 900m altitudes respectively or should exhibit more negative values. An explanation of this effect is the contribution of waters that flow from the river Strimona to the springs. This approach could correspond for ERA1 and ERA15 stations for Nestos river contribution. Regarding rest of stations, the mountain massif of Rhodope corresponds to an altitude of 1953m in Greece. This would explain, as in other areas, the influence of altitude in relation to the Rhodope Mountains. Specifically, THE1 station, which is very close to the border between Greece and Bulgaria, the altitude difference may be a sufficient explanation for δ 18 O values. The correlation between δ 2 H and δ 18 O is considered very good, while the corresponding equation is δd=5.1*δ 18 O (r 2 =0.94). Generally, the isotopic ratio of δ 2 Η/δ 18 O about 8 reflects meteoric waters of all water types where surface waters have not undergone significant evaporation before their entrance to the groundwater circulation. Unlike slopes ranging from 4 to 6 reflect isotopic relations δ 2 Η and δ 18 O where waters have suffered secondary evaporation [9]. As it has been already noted samples grouped clearly to three categories with respect to Cl - concentration. Within isotopic analysis these categories are minimized only in two: GROUP-I (ΤΡΑ1, PΟΤ1, ΜΥΡ, ΕRΑ6, ERT1) with mg/l Cl - and GROUP-IΙ (ΕRΑ-1, ERA-15, AGI-1, SID-1, THE-1, AGI-1[cold water]) with 7-231mg/l Cl -. The equation of GROUP-I and GROUP-II are δd=7.68*δ 18 O (r 2 =0.44) and δd=5.1*δ 18 O (r 2 =0.91) respectively (Figure 4). Figure 4. Isotopic composition (δ 18 Ο and D) of thermal waters in East Macedonia and Thrace area * sampling stations; + seawater; AGI1 cold water; _. _ GROUII trend line _ GROUP I trendline 4

6 Generally, the isotopic ratio of δ 2 Η/ δ 18 O about 8 reflects meteoric waters of all water types where surface waters have not undergone significant evaporation before their entrance to the groundwater circulation. Unlike slopes ranging from 4 to 6 reflect isotopic relations δ 2 Η and δ 18 O where waters have suffered secondary evaporation [9]. As it has been already noted samples grouped clearly to three categories with respect to Cl - concentration. Within isotopic analysis these categories are minimized only in two: GROUP-I (ΤΡΑ1, PΟΤ1, ΜΥΡ, ΕRΑ6, ERT1) with mg/l Cl - and GROUP-IΙ (ΕRΑ-1, ERA-15, AGI-1, SID-1, THE-1, AGI-1[cold water]) with 7-231mg/l Cl -. The equation of GROUP-I and GROUP-II are δd=7.68*δ 18 O (r 2 =0.44) and δd=5.1*δ 18 O-15.3 (r 2 =0.91) respectively (Figure 4). GROUPI presents a slope about 7.68 with weak correlation between the samples while the trend line coincides with seawater. This observation is in accordance with geochemical analysis where Cl/Br ratio and mass equation resulted in a clear marine contribution. Rest of samples from GROUPI (AGI-I, SOD-I, SID- cold water ) exhibit an enrichment of δ 18 Ο values with stable δd implying the interaction of geothermal solutions with the hosting rocks. This outcome is in consistence with their lower from seawater Mg/Cl ratio. GROUII presents a slope about 5.54 and strong correlation between samples. These samples concern Na-Cl-HCO 3 (ERA-1, ERA-15, THE-I), Na-Ca-HCO 3 (SID1) and Na-HCO 3 -SO 4 (AGI1). Isolating Na-Cl-HCO 3 chemical type it is observed that its slope is retained δd=5.19*δ 18 O This observation is probably attributable to the contribution of surface water that flows from Strimona river to the springs and the evaporation from Vegoritida lake. 4. Geothermometers For POT-1 station geothermometers correlate well resulting in temperatures that range between 205 C and 221 C. Unlike, ΤΗΕ1 station geothermometers presented a large variation with temperatures between 83 C and C. This could be attributable to the fact that an assumption that accompanies geothermometers probably failed. These assumptions are: (1) the equilibrium of deep geothermal water with rock (2) the correlation of temperature with the depth (3) the efficient presence of rocks in order to reach the saturation of the geothermal fluid with respect to the ingredients used in geothermometria (4) when water flows at the surface, a major new balance has to exist (5) there is no dilution or mixing between thermal and cold water. Moreover, Na-K-Ca geothermometer could result to incorrect values if there is a high CO 2 concentration or if fluid interacts with sediment during its path to the surface enriching fluid with chemical elements [10]. Na/K geothermometer could result to misleading temperatures if underground temperature is below 140 o C as affected by the process where albite replaces plagioclase feldspar in igneous rocks [10]. Therefore, isotopic geothermometer of Mizutani and Rafter [11] was used which based in the balance of δ 18 O as a result from interaction between the water and the sulfates. This geothermometer resulted to temperatures between 143 C and 144 C for all the above stations. 5. Conclusion Chemical and isotopic analysis were performed for geothermal water samples. Br-Cl, Na-Cl, Ca-Cl, B- Cl, Ca-Na, K-Cl, δ 18 O-δ 2 H diagram were used to identify possible marine contribution. Generally thermal waters are grouped [12] into the following categories: (1) TRA1, ERA6, ERT1 samples where present a Na-Cl type and elevated Cl- concentrations ( mg/l). Cl/Br ratio ranges between and 295 and 305 close enough to that of seawater implying the contribution of a marine end member something that is also reflected to the Cl/B vs Cl - diagram as well. According to the mass equation the contribution of this marine member is estimated between 24-44% with the Eratino (ERT1) station to present the higher ratio; (2) POT1, MYR, AKR1, ELF samples present slightly elevated Cl - concentrations ( mg/l). MYR, AKR1 stations are characterized by a Na-Cl water type while POT1, ELF stations by a Na-Cl-HCO 3 water type. Cl/Br ratio is generally lower than that of seawater ranging between The increase of Cl - concentrations without the parallel increase of Mg 2+ values as well as the similar behavior of Cl/B vs Cl - suggesting that the water-rock interaction process 5

7 is not pronounced but a small contribution of a marine end member is existed about 8-10%, as resulting by mass equation of Cl - and Br - ; (4) THE1, SID1, AGI samples present low Cl - concentrations (7-49mg/l) and Na-Cl-HCO 3, Na-Ca-HCO 3, Na-HCO 3.SO 4 chemical types respectively reflecting fresh waters. These samples are grouped together representing the deep continental part of study area; (5) ERA15, ERA1 samples present low Cl - concentration and Na-Cl-HCO 3. Isotopic analysis confirmed the above observations and further highlighted the role of Nestos and Strimonas river as well as Vgoritida lake. Isotopic geothermometer responded better than chemical to the geothermal field estimation. Acknowledgement(s) This research is part of the project entitled " Development of an integrated methodology and intelligent tool for the study and utilization of geothermal fields of the act: Industrial Research and Technology Development Program 2013" funded by the General Secretariat for Research and Technology. References [1] Dotsika, E.,Michelot, J.L., Origine et températures en profondeur des eaux thermals d'ikaria (Grèce). C. R. Acad. Sci. Paris 315 (II), [2] Dotsika, E., Poutoukis, D., Michelot, J.L., Raco, B., Natural tracers for identifying the origin of the thermal fluids emerging along the Aegean Volcanic arc (Greece): Evidence of Arc-TypeMagmaticWater (ATMW) participation. J. Volcanol. Geoth. Res. 179, [3] Henley, R.W., Ellis, A.J., Geothermal systems ancient and modern: a geochemical review. Earth-Sci. Rev. 19, Arnorsson, S., Geothermal systems in Iceland: structure and conceptual models. 1. High-temperature areas. Geothermics [4] Michelot, J.L., Dotsika, E., Fytikas, M., A hydrochemical and isotopic study of thermal waters of Lesbos Island (Greece). Geothermics 22, [5] Nicholson, K., Geothermal Fluids; Chemistry and Exploration Techniques. Springer, Berlin [6] Truesdell, A.H., Thompson, J.M., Coplen, T.B., Nehring, N.L, Janick, C.J., The origin of the Cerro Prieto geothermal brine. Geothermics 10 (3/4), [7] Arnorsson, S., Geothermal systems in Iceland: structure and conceptual models. 1. Hightemperature areas. Geothermics [8] Leontiadis I.L., Vergis S., Christodoulou Th., Isotope hydrology study of areas in Eastern Macedonia and Thrace, Northern Greece, Journal of Hydrology, Volume 182, Issues 1-4, July 1996, Pages 1-17 [9] Gat J.R., Chapter 1 Isotope Hydrology of Very Saline Lakes, In: A. Nissenbaum, Editor(s), Developments in Sedimentology, Elsevier, 1980, Volume 28, Pages 1-7 [10] Fytikas, M., Andritsos, N., Exploitation possibilities of the Sousaki Geothermal Field. Bulletin of the Greek Geological Society, vol. XXXVI, , 2008 (in Greek) [11] Mizutani, H., Rafter, T.A., Oxygen isotopic composition of sulfates: 3. Oxygen isotopic fractionation in the disulfate water system. N. Z. J. Sci. 12, [12] Dotsika, E., Lykoudis, S., Poutoukis, D., Spatial distribution of the isotopic composition of precipitation and spring water in Greece. Global and Planetary Change 71,

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