Diffusion of siderophile elements in iron-nickel alloys, with applications to iron meteorites

Experiments have been conducted at a wide range of temperatures and pressures to describe the diffusive behavior of several siderophile elements and phosphorus in an Fe90Ni10 alloy. The results from these experiments have implications for diffusive length scales in the early Earth as well as the deep Earth today.;Piston cylinder experiments at 1 GPa and 1175°C--1400°C revealed the following Arrhenius relations for Au, Pd, Cu, Re, Mo, and P: DAu=8E-4+/-9E-5m2 /sexp -309+/-24kJ/molRT DPd=7E-3+/-3E-3m2 /sexp -347+/-81kJ/molRT DCu=3E-5+/-5E-6m2 /sexp -270+/-22kJ/molRT DRe=1E-4+/-4E-5m2 /sexp -308+/-10kJ/molRT DMo=2E-2+/-7E-3m2 /exp-35 6+/-56kJ/molRT DP=8E-4+/-5E-5m2 /sexp -264+/-34kJ/molRT Multi-anvil experiments at 10GPa and 1100°C--1600°C yield the following Arrhenius relations for Au, Pd, and Re: DAu=4E-6+/-1E-5m2 /sexp -253+/-33kJ/molRT DPd=2E-6+/-2E-6m2 /sexp -257+/-16kJ/molRT DRe=5.5E-7+/-2E-6m 2/sexp -244+/-46kJ/molRT A study of pressure dependence on diffusion of Au, Pd, and Re at 1400°C and pressures from 1--∼25 GPa and P at 1300°C from 1--5 GPa yielded the following expressions for the activation volumes. DVAu=&parl0;3.0E-7+/- 2.6E-8&parr0;Pm3/mol DVPd=&parl0;5.9E-7+/-1.8E-8&parr0; Pm3/mol DVRe= 3.5E-7+/-4.3E-7m3 /mol DVP=5.9E-7+/-3.9E-7m 3/mol .;The diffusivities of these siderophile elements show a possible linear dependence on ionic radius in the metal. P behaves quite differently than the other elements studied. Its diffusivity tends to be about 3 orders of magnitude higher than the other elements, it shows a slightly lower activation energy at 1GPa, and a much weaker dependence on pressure than Au, Pd, and Re. P is inferred to diffuse via an interstitial mechanism, as opposed to lattice diffusion.;The results at 1GPa have important applications in meteorites. A model is developed with which siderophile element and Ni concentration profiles are simulated in two phases of FeNi alloy undergoing slow cooling to form the characteristic Widmanstatten texture seen in iron meteorites. Matching many simulated profiles to observed profiles in natural samples can give tighter constraints on the estimation of meteorite parent body cooling rates, and in turn, their sizes. A laser ablation ICP-MS technique is described by which siderophile element profiles can be measured in taenite lamellae of meteorites with the appropriate spatial resolution and detection limits that are necessary to use the numerical model effectively.