Plume-tree Structure Induced by Low-Viscosity Layers in the Upper Mantle

Deep-rooted mantle plumes are buoyant and hot upwellings that are considered a likely origin of surface intraplate volcanoes. Related large igneous provinces and hotspot tracks can be well described by the mantle plume model. Based on previous seismic tomography results and geodynamic modeling, mantle plumes have thin tails only a few hundred kilometers in diameter. However, the latest geophysical observations reveal not only the existence of broad and vertical conduits in the lower mantle but also the presence of plume bifurcations in the upper mantle, providing a new challenge to further understand the evolution of plume morphology. Here, developing a 3-D numerical model with spherical geometry, we demonstrate that a plume shaped like a tree, derived from a large thermal patch in the mantle transition zone, branches up to surface volcanoes due to the combined influence of weak layers in the asthenosphere and the mantle transition zone. Clusters of mantle plumes likely account for the simultaneous occurrence of multiple hotspot tracks in the Pacific and Atlantic Oceans. Meanwhile, the mantle plume wandering at a rate of ~ 1.5 cm/yr in the upper mantle without a strong mantle wind provides a new mechanism for hotspot motions, which have strong effects on the formation of surface hotspot tracks. Our model may provide a novel and comprehensive explanation for plume bifurcations, multiple hotspot tracks with divergent geochemical signatures and fast plume wandering in the upper mantle and therefore represents a significant advance for linking plume studies in seismology, geochemistry and plate reconstruction.