Plume Geometry and Rheology: General Patterns in Probabilistic Gravity Models

This study examines and compares 3D distributions of crustal and upper mantle density contrast with a set of geological and geophysical data for the heads of six plumes (Yellowstone, Emeishan, Cathaysia, Sea-of-Okhotsk, Maya–Selemdzha, and Indigirka–Kolyma plumes) down to 200 km depth. According to our data, the asthenospheric parts of the plumes have mushroom shapes, while the asthenospheric magmas are spreading out beneath the lithosphere bottom, less frequently beneath the crustal bottom. The plume heads become narrower at distances of 250–300 km from the central conduit to decrease to diameters of 200–300 km at depths of 100–120 km. In most of the cases, the plume lithospheric and crustal fragments are convex toward the ground surface. The uplifts are occasionally complicated with local depressions in the upper crust, which can be explained by subsidence of the domes of the structures above magma chambers in the subcrustal viscous layer and asthenosphere. Plumes are frequently associated with zones of lithosphere tension (rifts), resulting in linear zones of lower viscosity being mapped in the lower lithospheric and crustal cross sections of the plumes. The structural settings of the plumes under consideration here are controlled by boundaries of lithosphere plates and large segments of the second order. The identity of geometry and rheology in the plumes that were formed at different times (Triassic to Neogene), and in regions far removed from each other (Northeast Russia, Amur region, northwestern United States, South China, and Sea of Okhotsk), provide evidence of the universality of the tectonic settings that favor the penetration of mantle flows into the upper tectonic shells of the Earth. The foremost among these are tension zones in the lithosphere, especially areas where differently directed lithospheric faults intersect.