Overpressure build-up in mid-ocean ridge magma lenses

Mid-ocean ridge eruptions and hydrothermal circulation are thought to be fueled by sill-shaped axial melt lenses (AMLs) located a few km below seafloor. Multiple such bodies have now been seismically imaged within lower crustal mush zones. The short recurrence time of eruptions (~10 yrs) at fast-spreading ridges, as well as the considerable heat output of hydrothermal vents (~100 MW) both suggest that AMLs undergo magmatic replenishment at rates that match or exceed long-term rates of oceanic crust accretion. Repeated seismic imaging recently confirmed that AMLs can expand significantly in ~20 years. Lastly, distributed seafloor uplift (~10 cm/yr) indicative of inflation in sub-axial magma reservoirs has now been documented at two magmatically-robust ridge segments.

While observations point to highly dynamic AMLs on decadal time scales, the associated rates of magmatic inflation, and the underlying physics of spontaneous magmatic overpressurization remain elusive. This presentation will review existing and novel constraints on AML inflation dynamics, from the interpretation of seafloor geodetic data to the impact of overpressurization on hydrothermal output. These constraints will then be used to evaluate a range of candidate mechanisms, from volatile exsolution to decompaction below a permeability barrier.