Oct. 9, 2019,
noon - 1 p.m.
In this presentation I will firstly show results from numerical simulations of global mantle convection to explore the effects of melting on the thermo-chemical evolution of terrestrial bodies. I applied the models to investigate (i) how does melting-induced crustal production affects the interior state and surface behavior of an Earth-like planet, and (ii) the effects of intrusive versus extrusive magmatism on the surface tectonics and mantle cooling of a terrestrial planet. Results show that (i) melting-induced crustal production helps plate tectonics on Earth-like planets by strongly enhancing the mobility of the lid; (ii) high intrusion efficiencies (i.e. dominance of intrusion versus extrusion) lead to a new tectonic regime, named “plutonic-squishy lid” characterized by a set of strong plates separated by warm and weak regions generated by plutonism, and can cool the mantle more efficiently than volcanic eruptions for planets with no subduction in their history. In the second part of the talk I will focus on the present-day structure and dynamics of the Earth. Seismic images of Earth’s mantle have revealed changes in mantle structure between 400-1000 km depth. The structures at these depths appear to be different in nature from the lowermost mantle or the lithosphere. I demonstrate that the changes in structure are driven primarily by the reduced rate of sinking of subducted oceanic plate material in the western Pacific basin. Next, I use numerical models of mantle convection to demonstrate that the observed structures can be best explained by a relatively large increase in mantle viscosity between the upper mantle and lower mantle at 660 km depth or perhaps somewhat deeper, near 1000 km.