Mantle evolution in Venus due to magmatism and phase transitions: From punctuated layered convection to whole‐mantle convection

Abstract

A series of numerical models of magmatism and mantle convection with a stagnant lithosphere are developed to understand the mantle evolution in Venus. Magmatism is modeled as a permeable flow of basaltic magma generated by decompression melting, and the solid-state convection of mantle materials with temperature-dependent Newtonian rheology is affected by the garnet-perovskite transition and the postspinel transition. In our preferred models, the mantle evolves in two stages: The earlier stage is characterized by layered mantle convection punctuated by repeated bursts of hot material from the deep mantle to the surface. Mantle bursts induce vigorous magmatism and also cause the basaltic crust, enriched in heat-producing elements (HPEs), to recycle into the mantle. A part of the recycled basaltic crusts accumulates along the postspinel boundary to form a barrier, and this basalt barrier causes mantle convection to become layered. At a later stage, when the HPEs have already decayed, in contrast, the basalt barrier disappears and whole-mantle convection occurs more steadily. Mild magmatism is induced by small-scale partial melting at the base of the crust and hot plumes from the deep mantle. The internal heating by the HPEs that recycled into the mantle in the earlier stage allows the magmatism of the later stage to continue throughout the calculated history of mantle evolution. The two stages arise when the barrier effect of the postspinel transition is weak and the lithosphere is mechanically strong enough. The two-stage evolution model meshes with the observed history of magmatism and the lithosphere on Venus.

Themis Regio, Venus: Evidence for recent (?) volcanism from VIRTIS data

“…Stofan and Smrekar (2005) proposed this interpretation for corona-dominated topographic rises on Venus, such as Eastern and Central Eistla and Themis Regiones. Ogawa and Yanagisawa (2014) propose that the magmatic history of Venus can be explained by recycling of the crust that creates a basalt barrier at the upperlower mantle transition zone. When there is significant crust at the transition zone, convection is layered.…”

A positive feedback between magmatism and mantle upwelling in terrestrial planets: Implications for the Moon

“…The same as Figures g–i but for a model of the early evolution of the mantle in Venus calculated in Ogawa and Yanagisawa []. Here the Rayleigh number is 1.1 × 10 8 , about 100 times higher than the threshold for the MMU feedback.…”

“…The composition of the matrix is calculated from the mass balance equation. (See Appendix A5 of Ogawa [] for more detail).…”

“…Elucidating the control of planetary size over mantle dynamics that is behind this difference in magmatic history between planets is one of the most important issues in the study of the interior of terrestrial planets. To resolve this issue, here I extend the earlier numerical models of magmatism and mantle convection developed for Mars and Venus in Ogawa and Yanagisawa [, , ] (hereinafter called Papers 1, 2, and 3, respectively) to smaller planetary bodies, keeping the application of the model to the Moon in mind.…”

Mathematical Geosciences: Local Singularity Analysis of Nonlinear Earth Processes and Extreme Geo-Events

“…The episodicity of convection induced by the endothermic phase changes strongly depends on plate length, rheology, and Clapeyron slope (Zhong and Gurnis 1994). Ogawa and Yanagisawa (2014) have developed models with small Clapeyron slope −0.2 to −1 MPa/K for simulating convections from punctuated layered convection to whole-mantle convection in modeling mantle evolution on Venus due to magmatism and phase transitions. Their models indicate that the earlier stage layered mantle convection is punctuated by repeated bursts of hot material from the deep mantle to the surface.…”