Are terrestrial plumes from motionless plates analogues to Martian plumes feeding the giant shield volcanoes?

The near “one-plate” planet evolution of Mars has led to the edification of long-lasting giant shied volcanoes. 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. On Earth, where plate tectonic is active, most of them
are regenerated and recycled through convection. However, the Nubian and Antarctic plates could be considered as
poorly mobile surfaces of various thicknesses that are acting as conductive lids on top of Earth’s deeper convective
system. In these environments, volcanoes do not show any linear age progression at least for the last 30 Ma, but
constitute the sites of persistent, focused long-term magmatic activity, rather than a chain of volcanoes as observed
in fast-moving plate plume environments. Here, the near stationary absolute plate motion probably exerts a primary
control on volcanic processes, and more specifically, on the melting ones. The residual depleted mantle, that is left
behind by the melting processes, cannot be swept away from the melting locus. Over time, the thickening of this
near-stationary depleted layer progressively forces the termination of melting to higher depths, reducing the melt
production rate. Such a process gradually leads both to decreasing efficient melt extraction and increasing mantle
lithospheric-melt interactions. The accumulation of this refractory material also causes long-term fluctuations of
the volcanic activity, in generating long periods of quiescence. The presence of this residual mantle keel induces
over time a lateral flow deflection, which translates into a shift of future melting sites around it. This process gives
rise to the horseshoe-like shape of some volcanic islands on slow-moving plates (e.g. Cape Verde, Crozet). Finally,
the pronounced topographic swells/bulges observed in this environments may also be supported both by large scale
mantle upwelling and their residual mantle roots. Most of these processes are likely similar to those observed on
Martian giant shield volcanoes. The goal of this presentation will be to describe the essential characteristics of
intra-oceanic plumes on slow moving plates on the Earth and to point out their similarities with those of the large
shield volcanoes from the Tharsis region.