24. apríl - Araksan Ahmed Aden (PhD student, University of Iceland).
Titill: Hydrothermal fluid characterization from fluid inclusions in the Gale-Le-Koma and Asal-Fiale geothermal fields in the Asal-Ghoubbet rift, Republic of Djibouti
Tími: 12:30Staður: Askja, Fundarherbergi á 3ju hæð (herb. 367) og streymt á Zoom:
Listi yfir föstudagserindi Jarðvísindastofnunar og Norræna eldfjallasetursins.
Útdráttur:
High-temperature geothermal systems in active rifts commonly host hydrothermal fluids derived from seawater and/or meteoric water, modified by boiling, mixing, and fluid-rock interactions. However, surface sampling may alter reservoir signatures, and pristine fluids can be unavailable. This study constrains the origin and evolution of hydrothermal fluids in the ~1 Ma Asal-Ghoubbet rift using crystal-hosted fluid inclusions from recently drilled wells. The investigated wells include GLC1, targeting a shallow (∼400-700 m MD) reservoir in the Gale-Le-Koma field, and F1–F3, targeting a deep (>1900-2000 m MD) reservoir in the Asal-Fiale field, locally separated from a shallow reservoir by a seawater-driven cold zone. Fluid inclusions in secondary quartz, anhydrite, and plagioclase grains from drill cuttings were analyzed using petrography, microthermometry, Raman spectroscopy, and LA-ICP-MS. In GLC1 well, inclusions record temperatures of ~136-191°C and a wide salinity range, indicating progressive cooling to present-day conditions (~130 °C) and past boiling and/or mixing between ascending saline fluids and seawater. In the Asal-Fiale field, fluid inclusions in the shallow reservoir reveal transient high-temperature episodes (up to ~370°C) with moderate salinities, interpreted as isothermal mixing followed by cooling due to seawater ingress. Present-day conditions are best preserved in the F1 and F3 wells. The cold zone shows low current temperatures (~68°C) that are not recorded by fluid inclusions and alteration mineralization, suggesting a recent, fault-controlled seawater inflow, likely associated with the 1978 Ardoukôba rifting event. Fluid inclusions in the deep reservoir document high-temperature (>300°C) fluid circulation, phase separation, CO2-bearing vapor, consistent with magmatic volatile input. Fluid chemistry is primary controlled by seawater-basalt interaction, with additional effects from mixing and localized boiling. These findings improve the understanding of reservoir conditions, inform scaling and metal-transport risks, and support geothermal development in the Republic of Djibouti and similar rift systems.
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