Early Water on Mars Hindered Subduction‐Driven Plate Tectonics

Abstract

Mars lacks subduction‐driven plate tectonics, and the reason for this is poorly known. Here, we investigate whether early water on Mars inhibited long‐term sustained subduction by lowering the crustal density during metamorphism. We use numerical and thermodynamic modeling to estimate the subduction potential of the variably hydrated Martian crust. Our reference model, representative of the Hesperian (3.7–3.0 Ga) to early Amazonian (3.0–∼2.0 Ga), shows that hydration stabilized low‐density hydrous assemblages, driving the density contrast toward values that hindered subduction. In dry scenarios, subduction is predicted along cool Martian geotherms, contrasting with the lack of subduction‐driven tectonics on Mars. However, our wet models show that subduction was suppressed by minimal hydration (>0.45 wt% H ₂ O). We propose that the presence of water early in Mars history explains the lack of subduction‐driven plate tectonics. Our conclusions remain valid even when accounting for variations in crustal thickness between the northern and southern hemispheres as currently observed, as well as for the presence of a lithosphere comparable in thickness to the crust, as inferred for the Noachian (4.1–3.7 Ga). Our work reconciles Mars's tectonic quiescence with its hydrologically active past.