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Abstract. Geological carbon sequestration provides permanentCO2 storage to mitigate the current high concentration of CO2 inthe atmosphere. CO2 mineralization in basalts has been proven to be oneof the most secure storage options. For successful implementation and futureimprovements of this technology, the time-dependent deformation behavior ofreservoir rocks in the presence of reactive fluids needs to be studied indetail. We conducted load-stepping creep experiments on basalts from theCarbFix site (Iceland) under several pore fluid conditions (dry,H2O saturated and H2O + CO2 saturated) at temperature,T≈80 ∘C and effective pressure, Peff=50 MPa,during which we collected mechanical, acoustic and pore fluid chemistrydata. We observed transient creep at stresses as low as 11 % of thefailure strength. Acoustic emissions (AEs) correlated strongly with strainaccumulation, indicating that the creep deformation was a brittle process inagreement with microstructural observations. The rate and magnitude of AEswere higher in fluid-saturated experiments than in dry conditions. We inferthat the predominant mechanism governing creep deformation is time- andstress-dependent subcritical dilatant cracking. Our results suggest thatthe presence of aqueous fluids exerts first-order control on creepdeformation of basaltic rocks, while the composition of the fluids playsonly a secondary role under the studied conditions.