AN EXPERIMENTAL STUDY OF STRONTIUM AND LEAD DIFFUSION IN CALCITE, AND IMPLICATIONS FOR CARBONATE DIAGENESIS AND METAMORPHISM

Abstract

Chemical diffusion of Pb and Sr has been measured in natural calcite under anhydrous conditions. The source of diffusants for the Sr and Pb diffusion experiments were SrCO3 and PbO powders, respectively. Experiments were run in sealed silica capsules containing finely ground calcite to ensure stability of the single-crystal samples during diffusion anneals. Rutherford backscattering spectroscopy (RBS) was used to measure diffusion profiles. The following Arrhenius relations were obtained over the temperature range 440-800°C for Sr, 440-650° for Pb:DSr = 2.1 x 10-13 exp(-132 +/- 6 kJ mol-1/RT) m2 s-1DPb = 5.8 x 10-15 exp(-117 +/- 9 kJ mol-1/RT) m2 s-1Diffusion of Sr and Pb is relatively rapid in comparison to rates for these elements in other minerals, but fine-scale zoning and isotopic and chemical signatures many be retained in calcites under many conditions if diffusion is the dominant process affecting alteration.