Chemical and isotopic characterization of the thermal fluids emerging along the North\u2013Northeastern Greece

E. Dotsika,A. Arvanitis,M. Tassi,N. Kolios,P. Karalis,G. Diamantopoulos,E. Spyridonos,P. Dalampakis,J. L. Michelot,B. Raco

doi:10.1038/s41598-021-95656-6

Abstract

Hydrochemical and isotopic characteristics of fluids from major geothermal fields of middle/low temperature in N/NE Greece are examined [basins: Strymon River (SR), Nestos River Delta (ND), Xanthi–Komotini (XK), Loutros–Feres–Soufli (LFS) and Rhodope Massif]. The geodynamic context is reflected to isotopic/chemical composition of fluids, heat flow values and elevated CO2 concentrations in emitted fluids. B and Li are derived from leaching of the geothermal systems hosting rocks. δ18OH2O, δ18OSO4, δ13CCO2 values and chemical compositions of Cl, B and Li of geothermal discharges suggest two distinct source fluids. Fluids in SR exhibit high B/Cl and Li/Cl ratios, suggesting these constituents are derived from associated magmas of intermediate composition (andesitic rocks). Geothermal discharges in LFS exhibit low B/Cl and Li/Cl ratios, implying acid (rhyolitic) magmatism. δ13CCO2 and CO2/(CO2 + 105He) ratios in the west part, suggest fluids affected by addition of volatiles released from subducted marine sediments. For the eastern systems, these ratios suggest gas encountered in systems issued from mixing of crustal and mantle-derived volatiles. Isotopic geothermometers reflect, for the same direction, equilibrium processes more (LFS, XK) or less (SR) pronounced and discriminate the geothermal field from low to middle [SR, ND (Erasmio)] and middle to high enthalpy [ND (Eratino), LFS, XK].

Highlights

Isotope geochemistry, has greatly contributed in understanding geothermal systems since chemical and isotopic composition of geothermal fluids provides information on their origin, recharge areas, flow patterns, water–rock interaction processes and geothermal reservoir’s deep temperature[1,2]
On the basis of the Cl contents, they may be categorized as follows: Low Chloride waters: < 200 mg/l This group includes the thermal waters of Strymon River basin (SR) (NIG, SID, AGS, ACH and IRA), Nestos Delta basin (ND) (ERA) and LFS (FYL) basins
Some waters samples from Nigrita and Sidirokastro geothermal fields are localized in the group of fresh waters along the Local Meteoric Water Line for Greece (LMWL)[28] (Fig. 6), indicating a meteoric origin without the participation of seawater, as it is concluded by the geochemical analysis

Summary

Introduction

Isotope geochemistry, has greatly contributed in understanding geothermal systems since chemical and isotopic composition of geothermal fluids provides information on their origin, recharge areas, flow patterns, water–rock interaction processes and geothermal reservoir’s deep temperature[1,2]. Some waters samples from Nigrita and Sidirokastro geothermal fields are localized in the group of fresh waters along the Local Meteoric Water Line for Greece (LMWL)[28] (Fig. 6), indicating a meteoric origin without the participation of seawater, as it is concluded by the geochemical analysis.

Results

Conclusion