Multi-Physics Imaging of the Goban Spur Magma-Poor Rifted Margin: New Constraints on Breakup Processes Across the Continent–Ocean Transition

Magma-poor rifted margins record late-stage continental breakup characterised by extreme thinning, mantle exhumation and serpentinisation, and variable magmatic addition across the continent–ocean transition. Disentangling these processes remains challenging using seismic P-wave velocities alone, because serpentinisation and mafic additions can produce overlapping velocity signatures. Electrical resistivity provides a complementary constraint because serpentinisation is thought to increase conductivity, while mafic additions are expected to generate resistive structures.

In September 2023, we acquired a ~200 km multi-physics geophysical profile across the Goban Spur magma-poor rifted margin offshore Ireland, which records continental breakup and the opening of the Atlantic basin at ~100–125 Ma. We deployed 49 multi-sensor seafloor instruments, most of which recorded wide-angle controlled-source seismic, controlled-source electromagnetic (CSEM), and magnetotelluric (MT) data. All data were sampled at 250 Hz. The profile is collinear with two high-quality multichannel seismic (MCS) reflection profiles acquired in 2013 and 2024.

Seismic traveltime tomography images a sharp transition from >10 km-thick continental crust to an exhumed mantle domain where pristine peridotite velocities are reached at ~4 km below the seabed, implying the presence of a ~3-4 km-thick zone comprising of serpentinised peridotite beneath the thin (< 1 km) sediment cover. Additional tomographic constraints come from refracted arrivals in the MCS streamer data. This transition coincides with a lateral decrease in resistivity inferred from MT inversions. Toward the oceanward end of the profile, magnetic anomaly C33r marks the transition to oceanic crust; oceanward of C33r, velocities indicate a more complex structure than typical mature oceanic crust, remaining similar to those in the exhumed mantle domain. MT inversions at the oceanward end further reveal a shallow lithosphere–asthenosphere boundary (LAB) at ~55–60 km depth expressed as a sharp increase in conductivity, which we interpret as due to the presence of partial melt. This shallow LAB is consistent with independent surface-wave constraints and is potentially sustained by ongoing small-scale convection as suggested by geodynamic modelling. These multi-physics results provide new constraints on lithospheric structure and breakup processes at a magma-poor rifted margin.