Cratons are old and strong continental cores where the lithosphere is thick and remains largely undeformed for 2–3 b.y. Unlike typical cratons, the Wyoming craton underwent pervasive deformation ca. 80–55 Ma during the Laramide orogeny in the west-central United States, and has been subsequently encroached upon by the Yellowstone hotspot since 2.0 Ma. However, the mechanism for the deformation and the craton-hotspot interaction are not well understood. We present here a three-dimensional shear wave velocity model beneath the Wyoming craton constrained from Rayleigh wave data, which reveal new details about the cratonic lithosphere. The average lithosphere thickness beneath the craton is ∼150 km, significantly thinner than a normal cratonic root (>200 km). Continuous low velocities are observed beneath the Yellowstone hotspot and the Cheyenne belt. A low-velocity column is also present in the central-eastern craton at depths of 115–250 km. These low velocities can be explained by hot temperature and partial melting, implying mantle upwelling. A high-velocity anomaly with a dripping shape in central Wyoming extends to 200–250 km depth, indicating mantle downwelling and lithosphere erosion. Our model provides the first seismic evidence for complex small-scale mantle convection beneath the Wyoming craton. The convection probably developed during the subduction of the Farallon plate and has been reinforced by the Yellowstone hotspot. We propose that the combination of flat-slab subduction, small-scale convection, and hotspot activity can lead to massive destruction of a cratonic lithosphere.

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A billion years of tectonic history makes southeastern Canada and the northeastern United States an exciting area to investigate the evolution of continental lithosphere. Our study area comprises terranes with either Laurentian or Gondwanan provenance that accreted to eastern North America at different times. With the aim of resolving the isotropic velocity variations across the northern Phanerozoic Appalachians and the southeastern Proterozoic Grenville Province, we adopted a Rayleigh wave tomography technique that takes multipathing, scattering, and finite frequency effects into account. Our data sets include records of teleseismic earthquakes recorded by 71 broadband seismic stations over a 2‐year period. Our high‐resolution tomography models indicate significant (±3.5%) variations in shear wave velocity across different lithospheric domains, enabling us to discuss tectonic implications. In contrast to the Peri‐Laurentian zones, seismic signatures in the Peri‐Gondwanan domains are more complex and variable. Although systematic variations of seismic velocities across different tectonic zones are observed, we find no simple relation between the lithospheric thicknesses of different tectonic zones and their age. We interpret the lithosphere‐asthenosphere boundary in our study area, located at 70–120 km depth, with the thickest and fastest lithosphere beneath New Brunswick. We suggest that this relatively thicker lithosphere is due to a slab stacking process that occurred after flat subduction of a younger domain in the Late Silurian. Occurrence of flat subduction in the Late Silurian in the northern Appalachians is also supported by geochemical and paleomagnetic evidence.

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