Waveform tomography of the Earth’s continents: Lithospheric structure and evolution and their controls on seismicity, magmatism and natural resources

The structure and evolution of the lithosphere and underlying mantle control tectonics, magmatism, and natural resource development and distribution. Seismic tomography offers essential information on mantle temperature, the thickness and strength of the lithosphere, and the convection below it. Here, we report on the completion of a series of continent- and plate-scale waveform tomography studies using the automated multimode inversion of surface and S-wave waveforms. Together, the models cover all of the Earth’s continents and their surroundings and reveal a fascinating diversity of structures, while also indicating common mechanisms of lithospheric dynamics and evolution. Each model used global data coverage that was maximised witin the hemisphere centred at the continent. Structural information was extracted from Rayleigh waves and S and multiple S waves on over a million vertical-component-seismogram waveform fits. The effects of errors were minimised by statistical and targeted outlier analyses and the removal of the least mutually consistent data. The models advance the resolution of the imaging compared to the state of the art at the scale of the continents.

Cratonic lithosphere on all continents shows complexities and fragmentation. The lithosphere beneath most diamondiferous kimberlites—originally emplaced on thick cratonic lithosphere—is still thick at present. Relatively low seismic velocities at kimberlite locations are indicative of craton-lithosphere thinning and are detected at multiple locations in all continents with known kimberlites. Cenozoic basalts are found exclusively where the lithosphere is observed to be thin. Beneath some of the volcanic regions, low-velocity anomalies extend deep into the mantle, consistent with deep-mantle upwellings feeding the magmatism. Sediment-hosted metal deposits tend to be located near contrasts in the thickness of the lithosphere, including both craton boundaries and other substantial heterogeneities. Intraplate seismicity is controlled by plate-boundary stresses and by the lateral variations of the lithospheric thickness and strength. Areas with relatively thin lithosphere localise deformation and seismicity, provided that sufficient tectonic stress is transmitted into the plate interior.

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