Variable initial zoning profiles and Fe-Mg diffusion coefficients for olivine: Effects on cooling rates calculated by diffusion modeling in a pallasite

Because chemical zoning of minerals contains information about the thermal history of the parent body, the cooling rate or burial depth can be calculated by solving the diffusion equation. Several factors influence the results of these calculations. We evaluated the cooling rate (and burial depth) calculated by using different initial (starting) zoning profiles and different diffusion coefficients on the basis of the Fe-Mg chemical zoning profile observed for pallasite (Esquel) olivine. Uncertainties in initial compositional profile and Fe-Mg diffusion coefficient in olivine both lead to error in model cooling rates. Discrepancies between different experimentally determined diffusion coefficients lead to uncertainties in model cooling rate that exceed those due to initial zoning profiles by one order of magnitude. These results highlight the need for accurate determination of diffusion coefficients in olivine.