Geothermal potential and origin of natural thermal fluids in the northern Lake Abaya area, Main Ethiopian Rift, East Africa

Abstract

In this study, the occurrence, chemical composition, origin and geothermal significance of thermal springs and fumaroles naturally discharging in the area located north of the Lake Abaya (western margin of the Main Ethiopian Rift, East Africa) are reviewed in relation with recent tectonics. All thermal springs showed a dominantly Na-HCO 3 composition, consistent with observations dating from at least 1972, and most of them displayed a narrow range of δD and δ 18 O isotopic compositions for water similar to regional meteoric origins. These observations suggest that water-rock interaction processes occur in all aquifers and dominate the contributions of water that actively circulate within thermal fluids, and also suggest a similar elevation of groundwater recharge throughout the study area. Most of the thermal springs are dominated by a CO 2 -rich gas phase and discharge along the active faults bordering the western edge of the Main Ethiopian Rift valley. The δ 13 C values of CO 2 and the 3 He/ 4 He isotopic ratios are consistent with the presence of mantle-derived fluids similar to what is observed in many other areas along the kinematically active African Rift, especially within Ethiopia. The application of geothermometric techniques in the liquid and the gas phases suggests the presence of a deep reservoir in which the fluids equilibrated at a maximum temperature of approximately 180°C. Additionally, the presence of fumaroles at boiling temperatures and water/mud boiling pools in several places suggests that the geothermal reservoir is positioned at a relatively shallow depth and likely located in the western side of the study area. The analysis of data collected throughout time reveals that the waters of Lake Abaya have experienced an increase in salinity of 20% paralleled contemporaneously with a decrease in pH and δ 18 O and δD of water in the last 40 years; these changes do not appear to be related to climate changeinduced increases in temperature or evaporation at the global scale.

Seismicity and Crustal Structure of the Southern Main Ethiopian Rift: New Evidence From Lake Abaya

“…Cross sections through cluster 1 (Figure 10), which lies at the boundary between the central and southern MER (Figure 1), do not unambiguously delineate a simple, single fault plane associated with the western border fault system of the MER. Minissale et al (2017) found that the chemistry of thermal springs and fumaroles discharging naturally in the area immediately to the north of Lake Abaya is dominated by a 2 CO -rich gas phase and discharges along the active faults bordering the western edge of the MER. Cluster 1 is therefore readily explained by deformation associated with upper crustal magmatic fluid migration, akin to the central and northern MER (e.g., Keir et al, 2006).…”

Geochemical Evolution of Fluoride and Implication for F− Enrichment in Groundwater: Example from the Bilate River Basin of Southern Main Ethiopian Rift

“…In relation to the active fault zone, many thermal springs emerge in the area particularly in tectonically active northern Abaya in the rift floor. The thermal springs discharge within the rift floor along the north -northeast to south-southwest (NNE-SSW) trending faults [42] that emerge at varying elevations. Thermal springs in the northern lake Abaya area characterized by a temperature ranging from 35 to 95 • C and Na-HCO 3 type [42] with a TDS in the range of 1000-2500 mg/L.…”

Water-rock interaction, formation and circulation mechanism of highly bicarbonate groundwater in the northwestern geothermal prospects of Rwanda

“…Hydrogeochemical behaviors of thermal and non-thermal groundwater can be characterized using plots of various ions contents against electric conductivity or salinity as TDS (Delalande et al, 2008;Minissale et al, 2017). In Fig.…”