Are plumes on motionless plates analogues to Martian plume feeding the giant shield volcanoes?

The near “one-plate” planet evolution of Mars has led to the edification of long-lasting giant shied volcanoes, which dominate the topography of its western hemisphere. Unlike the Earth, Mars would have been a transient convecting planet, where plate tectonic would have possibly acted only during the first hundreds of million years of its history. Most of the Martian magmatic activity would be very old (Noachian) and has been preserved compared to the Earth in the near-absence of crustal recycling. Recent volcanic resurgence occurred in the two main Martian volcanic provinces, so-called Tharsis and Elysium. Although the large igneous magmatic provinces of Mars bear some geomorphological similarities with terrestrial oceanic plateaus, they distinguish themself by their larger scale-size. Their accretion, which is vertical due to the absence of lateral plate movement and crustal recycling, loads the lithosphere and causes lithospheric flexure, deformation and edifice flank failure. Underlying these huge volcanoes, the lithosphere might reach a thickness up to 150 km. The thickening of the lithospheric lid over time will have increased the final melting depth and thereby reduced the mean melting degree. Such kind of lithospheric processes are commonly observed in near stationary plate plume settings. However, while the Hawaiian Islands are located on a fast-moving plate (i.e. pacific, 7-8 cm/yr), Hawaiian hotspot intraplate magmatic activity has been commonly considered as some of the best analogs to that of observed on Mars. However, intraplate oceanic volcanism at slow moving plates such as Crozet or Cape Verde islands might constitute a better analog. As on Mars, volcanoes at motionless plates do not show any linear age progression, but constitute the sites of persistent, long-term magmatic activity. Because the lithosphere lid is near stagnant in these areas, the melting mantle region concentrates its products in a single area, rather than having them spread out as observed in fast-moving plate plume environment such as the Hawaiian-Emperor chain. The melt products accrete vertically into huge accumulation, generating oceanic swell heights unusually shallow for their ages. The loading of the lithosphere by the volcanic accumulations may cause flexural deformation and/or edifice collapse. These processes are likely similar to those observed on Mars. The goal of this presentation will be to describe the essential characteristics of intra-oceanic plumes on slow moving plates on the Earth and compare them to large shield volcanoes from the Tharsis region.