Seismologists have imaged a variety of geometries fast anomalies beneath subduction zones. These anomalies have been interpreted as deformed subducted oceanic lithosphere lying atop the base of the transition zone at some locations and subducted oceanic lithosphere traversing the transition zone with little apparent resistance at other locations. The investigators will investigate how the equation of state (i.e., density as a function of pressure, temperature, and composition) impacts the dynamics and morphology of subducted oceanic lithosphere. While a number of studies have shown that the morphology of subducted oceanic crust is controlled by the evolution of the plate boundary at the surface, the investigators have shown that the material properties and phase changes in the transition zone also have a significant impact on the morphology of subducted material. This research will bring together laboratory measurements of mineral properties with mantle convection calculations. Most compressible convection calculations currently use a simplified equation of state that is thermodynamically inconsistent and the first-order question that will be addressed is when and whether it is justified to use a simple equation of state. A second question is which parameters (e.g., slab strength, Clapyron slope of the transition zone phase transformations, slab age, plate velocity, trench migration) control the transition from flat lying slabs to penetrating slabs. The third component of this work is to assess which minerals and specific parameters in the thermodynamic database have the most significant effect on the dynamics of subduction. This provides guidance to the mineral physics research community as to which parameter(s) have the most significant influence on the dynamics of subduction. This will provide feedback as to which parameters to focus on improving measurements.
This proposal will develop a clearly documented, modular, software package that will provide the thermodynamic properties of a mantle material at a given pressure and temperature. The goal is to enable future researchers to update elements of the thermodynamic database as new information becomes available or to perform parameter study investigations by systematically changing specific elements of the thermodynamic database. This software will be developed to interface with current and future mantle convection codes and will be made available to the research community through the Computational Infrastructure for Geodynamics website.
