Fault scarps and tectonic strain in young volcanic seafloor

Fault scarps at Mid-Ocean Ridges (MOR) are recognizable on the seafloor, and often measured to estimate the tectonic component of plate divergence. This estimate, based on linear fault scarp parameters, is referred to here as apparent tectonic strain (ATS). However, ATS may differ from the actual tectonic strain at a lithosphere scale. This is clear at detachment faults at magma-poor slow-ultraslow spreading ridges that do not correspond to linear scarps yet accommodate very high strain. Here we study fault scarps in young volcanic MOR seafloor, using high-resolution (1–2 m) bathymetry data of 8 sites with spreading rates of 14–110 km/Ma. Our results show a weak correlation between ATS and factors such as spreading rate, melt flux, or thermal regime, challenging the use of ATS as a proxy for the MOR tectonic component of plate divergence. Instead, ATS is time-dependent and heterogeneous spatially, controlled by the frequency and size of dike intrusions with associated faults and volcanic eruptions that resurface the seafloor and cover faults. Our findings also have implications for estimates of tectonic extension in subaerial volcanic rifting systems that undergo similar processes.