Adam F. Holt

Hot upwelling conduit beneath the Atlas Mountains, Morocco

The Atlas Mountains of Morocco display high topography, no deep crustal root, and regions of localized Cenozoic alkaline volcanism. Previous seismic imaging and geophysical studies have implied a hot mantle upwelling as the source of the volcanism and high elevation. However, the existence, shape, and physical properties of an associated mantle anomaly are debated. Here we use seismic waveform analysis from a broadband deployment and geodynamic modeling to define the physical properties and morphology of the anomaly. The imaged low-velocity structure extends to ~200 km beneath the Atlas and appears ~350 K hotter than the ambient mantle with possible partial melting. It includes a lateral conduit, which suggests that the Quaternary volcanism arises from the upper mantle. Moreover, the shape and temperature of the imaged anomaly indicate that the unusually high topography of the Atlas Mountains is due to active mantle support.

Overriding plate thickness control on subducting plate curvature

Subducting plate (SP) curvature exerts a key control on the amount of bending dissipation associated with subduction, and the magnitude of the subduction-resisting bending force. However, the factors controlling the development of SP curvature are not well understood. We use numerical models to quantify the role of SP rheology on the minimum radius of curvature, Rmin. We find that Rmin depends strongly on the SP thickness when the rheology is viscous. This dependence is substantially reduced when the SP behaves plastically, in line with the lack of correlation between Rmin and SP thickness on Earth. In contrast, plasticity leads to a strong positive correlation between Rmin and the overriding plate (OP) thickness. Using an analysis of Rmin versus OP thickness, we show that such a positive correlation exists on Earth. This suggests that OP structure, in conjunction with SP plasticity, is crucial in generating slab curvature systematics on Earth.