09:00 〜 09:15
[PPS04-06] An extrapolation of mantle dynamics in Mars to Venus
★Invited Papers
キーワード：金星、火成活動、マントル対流、数値シミュレーション
I extrapolate a numerical model of mantle evolution that accounts for the volcanic history of Mars to Venus. The modeled Martian mantle evolves in four stages: an extensive magmatism that is caused by a high initial mantle temperature makes the mantle compositionally stratified on Stage I; the mantle becomes dormant for several hundred million years because of the mantle stratification on Stage II; partially molten plumes grow and ascend through the stratified mantle owing to melt-buoyancy to cause an episodic plume volcanism and to stir the mantle on Stage III; the plume magmatism subsides on Stage IV. The volcanism of Stage III accounts for the active Martian volcanism from the late Noachian to the Hesperian. When the mantle depth is increased to the value appropriate for Venus, the magmatism of Stage III continues for a longer period because of the larger heat capacity of the mantle. The magmatism causes a severe deformation of the lithosphere throughout the calculated history. When the solid-solid phase transitions at the top of the lower mantle is also considered, the volcanism on Stage III becomes more extensive and episodic. The phase transitions induce a layer of recycled basaltic materials, or the basalt-barrier, at the top of the lower mantle to impede the convective flow across the phase boundaries. Partially molten plumes are, however, occasionally generated in the upper mantle, and their melt-buoyancy massively pulls up the hot materials in the lower mantle to cause an extensive magmatism. This extensive magmatism severely deforms the crust, as observed for the tessera terrains on Venus. As the heat producing elements in the mantle decay and are extracted from the mantle by magmatism, however, the basalt barrier becomes fainter. Mantle convection becomes steadier, the deformation of the lithosphere becomes smaller, and only small melt-pockets are generated sporadically just beneath the crust to cause volcanic activities. This volcanism and small deformation of the lithosphere are consistent with the observed features of volcanic plains on Venus.