Smith Lecture: Modeling the Effects of Thermodynamic Properties on Slab Evolution
Seismic tomography images of subduction zones show that some subducting slabs, such as those in Izu-Bonin and Tonga, stagnate in the mantle transition zone while others, such as those in Central America and Java, sink into the lower mantle without much apparent resistance. Further, those that travel into the lower mantle seem to thicken with depth. There are extensive laboratory analogue and numerical modeling studies that explore the roles of various factors, such as slab buoyancy, mantle rheology, slab strength, trench motion, and slab dip, in controlling the geometrical evolution of subducting slabs. One aspect that is less explored is the role of thermodynamic properties, such as density, thermal diffusivity, thermal expansivity, and heat capacity, of the mantle minerals. The spatial variations in these properties associated with pressure, temperature, and phase changes influence mantle convection and slab evolution, but in many of the earlier studies of slab evolution these properties are assumed uniform. In this study, we develop a numerical geodynamic model that incorporates the thermodynamically self-consistent properties of the mantle minerals and investigate the influence of the properties on the slab evolution. Our results show that incorporation of the effects of thermodynamic properties can lead to a notably different slab behavior in geodynamic models and is important to simulating and understanding the slab evolution.