We currently have a limited understanding of the tectonic framework that governs Venus. Schubert and Sandwell (1995) identified over 10,000 km of possible subduction sites at both coronae and chasmata rift zones. Previous numerical and experimental studies have shown the viability of regional-scale lithospheric recycling via plume-lithosphere interactions at coronae, yet little work has been done to study the possibility of resurfacing initiated at Venusian rift zones. We created 2D numerical models to test if and how regional-scale resurfacing could be initiated at a lateral lithospheric discontinuity. We observed several instances of peel-back delamination - a form of lithospheric recycling in which the dense lithospheric mantle decouples and peels away from the weak, initially 30 km-thick crust, leaving behind a hot, thinned layer of crust at the surface. Delamination initiation is driven by the negative buoyancy of the lithospheric mantle and is resisted by the coupling of the plate across the Moho, the significant positive buoyancy of the crust arising from a range of crustal densities, and the viscous strength of the plate. Initial plate bending promotes yielding and weakening in the crust, which is crucial to allow decoupling of the crust and lithospheric mantle. When there is sufficient excess negative buoyancy in the lithospheric mantle, both positively and negatively buoyant plates may undergo delamination. Following a delamination event, the emplacement of hot, buoyant asthenosphere beneath the crust may have consequences for regional-scale volcanism and local tectonic deformation on Venus within the context of the regional equilibrium resurfacing hypothesis.

The rheological properties of Earth’s lower mantle are key for mantle dynamics and planetary evolution. The main rock-forming minerals in the lower mantle are bridgmanite (Br) and smaller amounts of ferropericlase (Fp). Previous work has suggested that the large differences in viscosity between these minerals greatly affect the bulk rock rheology. The resulting effective rheology becomes highly strain-dependent as weaker Fp minerals become elongated and eventually interconnected. This implies that strain localization may occur in Earth’s lower mantle. So far, there have been no studies on global-scale mantle convection in the presence of such strain-weakening (SW) rheology. Here, we present 2D numerical models of thermo-chemical convection in spherical annulus geometry including a new strain-dependent rheology formulation for lower mantle materials, combining rheological weakening and healing terms. We find that SW rheology has several direct and indirect effects on mantle convection. The most notable direct effect is the changing dynamics of weakened plume channels as well as the formation of larger thermochemical piles at the base of the mantle. The weakened plume conduits act as lubrication channels in the mantle and exhibit a lower thermal anomaly. SW rheology also reduces the overall viscosity, notable in terms of increasing convective vigor and core-mantle boundary (CMB) heat flux. Finally, we put our results into context with existing hypotheses on the style of mantle convection and mixing. Most importantly, we suggest that the new kind of plume dynamics may explain the discrepancy between expected and observed thermal anomalies of deep-seated mantle plumes on Earth.