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Abstract Detecting old hotspot tracks in a stable continent remains challenging because of the lack of volcano chains on the surface and the fade of thermal anomalies with time. The northeastern American continent moved over the Cape Verde and the Great Meteor hotspots during 300–100 Ma. However, only the latter was confirmed by kimberlites and seismic velocity models. Our new 3D anisotropic model in northeastern America reveals strong positive radial anisotropy anomalies in the eastern Great Lakes, central Pennsylvania, and northwestern Virginia. These anomalies follow the Cape Verde hotspot track, providing the first geophysical evidence for the hotspot. A circular pattern of azimuthal anisotropy is also observed in the eastern Great Lakes and may be related to the Cape Verde plume activity. The plume was under the Great Lakes during 300–200 Ma and probably caused lithosphere thinning and low topography needed for forming the Lakes during the glacial era. 

Southern Alaska is a collage of accreted terranes. The deformation history of accreted terranes and the geometric history of their bounding faults reflect both inherited features and associated convergent margin events. We employ S-to-P receiver functions on multiple dense (<20km spacing) arrays of broadband seismometers across southern Alaska to investigate signals of dynamic tectonic activity. An inboard-dipping (∼15∘) boundary is imaged aligning with the trace of the Border Ranges Fault, which is interpreted as an unrotated inboard-dipping paleo-subduction (Mesozoic) interface. This observation, along with previous seismic imaging of the Border Ranges Fault and the next outboard terrane-bounding fault, the Contact Fault, buttresses a known history of convergent tectonics that varies along the margin. Large (>10 km) crustal thickness offsets imaged across both the Denali Fault system and the Eureka Creek Fault support a Mesozoic-to-Present inboard-dipping (east and northward) subduction polarity in the region. Additionally, our imaging reveals a significant velocity increase with depth at ∼25km beneath the Copper River Basin, which we interpret as the top of a region of active underplating and/or intrusion of basaltic magmatism. This feature may be related to the generation of a newWrangell Volcanic Field volcano, resulting from the underlying tear in the subducting slab. 

The asthenosphere plays a fundamental role in present-day plate tectonics as its low viscosity controls how convection in the mantle below it is expressed at the Earth’s surface above. The origin of the asthenosphere, including the role of partial melting in reducing its viscosity and facilitating deformation, remains unclear. Here we analysed receiver-function data from globally distributed seismic stations to image the lower reaches of the asthenospheric low-seismic-velocity zone. We present globally widespread evidence for a positive seismic-velocity gradient at depths of ~150 km, which represents the base of a particularly low-velocity zone within the asthenosphere. This boundary is most commonly detected in regions with elevated upper-mantle temperatures and is best modelled as the base of a partially molten layer. The presence of the boundary showed no correlation with radial seismic anisotropy, which represents accumulated mantle strain, indicating that the inferred partial melt has no substantial effect on the large-scale viscosity of the asthenosphere. These results imply the presence of a globally extensive, partially molten zone embedded within the asthenosphere, but that low asthenospheric viscosity is controlled primarily by gradual pressure and temperature variations with depth.