Geochemical, multi-isotopic studies and geothermal potential evaluation of the complex Djibouti volcanic aquifer (republic of Djibouti)

Waters from the Djiboutian Afar: A Review of Strontium Isotopic Composition and a Comparison with Ethiopian Waters and Red Sea Brines

“…The mean strontium isotope ratio of the waters collected in the Hanlé-Gaggadé plain is 0.70595 ± 0.00070 (Table 1), which is at the central value of all of the previously investigated groundwater and basalts collected to date in Djibouti. Indeed, excluding those samples that were clearly mixed with seawater, the thermal and non-thermal waters from Djibouti studied to date show a strontium isotope ratio range of 0.70367 < 87 Sr/ 86 Sr < 0.70702 [20,[26][27][28][29], which is very close to the range of the Djiboutian basalts. Waters and rocks from the MER and flood basalts of the Ethiopian plateau show similar ranges of 0.70404 < 87 Sr/ 86 Sr < 0.70808 [39][40][41] and 0.70318 < 87 Sr/ 86 Sr < 0.70665 [30,42], respectively.…”

“…Water samples from 12 sampling sites in the Hanlé and Gaggadé plains were collected ( Figure 1 and the Google Earth map in the Supplementary File S1). The sampling procedure and the physicochemical analysis on site (temperature, pH, electrical conductivity) and in the laboratory (quadrupole ICP-MS determination of Sr concentration) are described in detail elsewhere [20]. Water aliquots dedicated to the determination of the 87 Sr/ 86 Sr ratio were filtered through 0.45 µm membrane filters (Millipore, Burlington, MA, USA) and acidified to pH < 2 with Suprapur ® HNO 3 (Merck, Kenilworth, NJ, USA) before being collected in 250 ml polyethene containers.…”

“…Afar [20,[26][27][28][29], the Ethiopian MER [39,40], and the Ethiopian Northern plateau [41]. Solid curves Figure 2.…”

“…In this study, we summarise and reinterpret the main results of the groundwater studies in Djibouti concerning the 87 Sr/ 86 Sr data [20,[26][27][28][29], comparing these with other data from the literature that come from neighbouring areas of active rifting (mainly the Main Ethiopia Rift and the Red Sea), and presenting new preliminary data on groundwater from the Hanlé-Gaggadé plains.…”

“…For the strontium isotopes ( 87 Sr/ 86 Sr) to be used successfully as a natural tracer in ground and surface waters, the isotope ratios of the potential endmembers must be distinct. If potential endmembers have distinct Sr isotopic ratios, Sr isotopes can be used to identify waters interacting with rocks from specific stratigraphic units [11,14,[16][17][18][19] and can even be used as sensitive indicators of seawater intrusion [20][21][22] or minute amounts of contamination [23][24][25].…”