S. Xie and P. J. Tackley $^{a}$
$^{a}$ Department of Earth and Space Sciences, University of California, Los Angeles, CA 90095, USA.
To better understand the maintaining and destroying of the geochemical reservoirs in the Earth's mantle, we have numerically investigated the mixing properties of 2-D compressible mantle convection in cylindrical geometry. The effects of the variable viscosity, plate tectonics, and heating mode on the survival of the geochemical heterogeneity are systematically examined. Blocks of tracers are injected into the mantle flow to study the lateral dispersion (which is relevant to the long-term survival of lateral geochemical anomalies). The strain distribution is tracked to determine stretching (stirring) of heterogeneities. The tracer dispersion function is employed to quantitatively measure the horizontal mixing properties of the mantle. Other quantities such as Lyapunov exponents, mixing time scales, and 2-particle correlation functions are also utilized to quantify the mixing process. While previous studies have disagreed as to whether laminar mixing or chaotic mixing are more appropriate in Earth's mantle, turbulent mixing regime is typically observed in our study. The key focus here is how greater physical realism affects mixing. Our study demonstrates that plate tectonics, heating mode, and variable viscosity influence the lateral mixing process. More realism does not necessarily cause much more rapid lateral mixing. For example, the introduction of internal heat and depth-dependent viscosity reduces lateral mixing. Plate tectonics also help to reduce lateral mixing efficiency.