Radial dike formation on Venus: Insights from models of uplift, flexure and magmatism

Giant radiating dike swarms on Venus are geomorphic manifestations of deep-seated volcano-tectonic processes. Through an initial series of experiments we assess if these features can be explained as a product of the relationship between magmatism and the flexural stress state caused by lithospheric uplift (due to a rising mantle diapir, plume or underplating processes) using gravitationally loaded, axisymmetric, elastic finite element models. Magma chambers situated in the upper (extensional) lithosphere fail at or near the crest, redirecting magma vertically into radially aligned dikes, but these are expected to feed surface eruptions; conditions promoting lateral propagation of dikes do not occur. Magma chambers located in the lower (compressional) lithosphere are predicted to generate horizontal intrusions (sills) upon midsection failure. When both uplift (from basal loading) and magmatic surface loading (from edifice growth) are introduced in sequence at discrete times, however, conditions that promote shallow lateral propagation of magma within radial dikes are created: (1) as magma from shallow reservoirs ascends and erupts, surface-loading volcanic edifices can form; (2) as the vertical loads increase, flexing the lithosphere downward, high compressional stresses produced within the edifice create a shallow stress barrier that makes it increasingly difficult for magma to complete the process of ascent and eruption; and then (3) stresses acting on dikes ascending from a reservoir toward the surface will thus increasingly favor fracture along their lateral margins, redirecting magma through radial dikes toward distal regions at shallow depth. Our results are consistent with observed patterns of laterally extensive dike systems at volcanic centers such as Mbokomu Mons and Becuma Mons. The models thus provide a robust mechanical explanation that for the first time links lithosphere flexure and reservoir pressurization to the ascent and lateral spreading of magma through radial dike systems on Venus, thereby providing key new spatial and temporal insights into an important magmatic process operating on multiple terrestrial planets.