The IMPULSE experiment: New oceanic crustal record of thermal plume pulsing of Earth’s strongest mantle plume

Thermal pulsing is thought to be a characteristic process of major mantle convection cells.  Seafloor features near Iceland, known as the "V-Shaped Ridges" (VSRs), may comprise the best record of thermal plume pulsing.  However, a satisfactory test of this thermal plume pulsing model has been compromised by the lack of suitable geophysical and geochemical datasets from the VSRs.  Here, we present the first full crustal seismic image of multiple complete VSR cycles.  In 2024, the IMPULSE experiment acquired an approximately 400 km long profile that straddles the Reykjanes Ridge spreading axis and several V-Shaped Ridge/Trough cycles spanning over 18 million years.  Traveltime picks for crustal and upper mantle refractions and PmP wide-angle Moho reflections were inverted using the TOMO2D software package to obtain crustal thickness as well as crustal and upper mantle seismic velocity.  The results show crustal thickness variations that correlate with VSR geometry.  They also reveal seismic velocity variations which indicate fluctuations in mineralogy of the lower crustal cumulates that correlate with the VSRs.  Mid-ocean ridge basalts sampled by International Ocean Drilling Program Expedition 395 at five sites along the seismic profile show trace element variations that correlate with the VSRs.  Significantly, we have imaged both conjugate flanks of the spreading axis along a plate spreading flowline.  Comparison of conjugate crustal thickness and structure permits us to disentangle primary melt supply processes from asymmetric crustal accretion processes.  The combined geophysical and geochemical dataset supports a model in which the VSRs form when thermal plume pulsing causes fluctuations in the volume and composition of magma supplied to the mid-oceanic ridge, and crustal accretion processes related to oblique spreading at variable rate then modify VSR morphology in different locations.