Thermo‐Mechanical State of Ultraslow‐Spreading Ridges With a Transient Magma Supply

The thermal structure of mid-ocean ridge axes is a critical control on the mechanical properties young lithosphere and modulates faulting styles that shape Earth's seafloor. Models balance steady input magmatic heat with vigorous hydrothermal output are generally successful at explaining state magmatically robust ridges. However, magma supply ultraslow spreading ridges often subdued highly episodic, depth-extent vigor circulation in these settings remain poorly known, requiring modifications to standard magmatic-hydrothermal paradigm. We develop models couple repeated intrusions convection permeable domain whose boundaries controlled by extent grain-scale cracking. Our simulations reveal decreasing trends venting temperatures increasing intrusion periodicity, as well permeability. model explains seismically inferred depth (∼10 km) brittle-ductile transition MORB crystallization Mid-Cayman Spreading Center invoking sills every 20–50 kyrs, depending their size. Doubling this periodicity predicts thicker (∼15 seismogenic layer lower-temperature venting, observed Southwest Indian Ridge (SWIR) 64˚E. if fluid not possible below ∼6 km, our requires high-temperature (e.g., Longqi SWIR 49.7˚E) be fueled shallow episodic into long-term convective region, which maintain high-output for most few tens kyrs.