Multipath diffusion: A general numerical model

Thermochronology in Orogenic Systems

“…Unfortunately, natural samples contain internal imperfections, such as subgrain boundaries or line defects formed by dislocation arrays, which can enhance or retard diffusivity. This suggests that a simple and reasonable conceptual model for isotope migration in natural crystals is one that involves interactive diffusion along multiple pathways at different rates (e.g., Lee, 1995;Lee and Aldama, 1992). An alternative to this 'multipath' model, referred to by Lovera et al (1989) as the 'multidiffusion domain' model, regards a crystal as a collection of discrete, noninteractive domains of different size with different volume diffusion characteristics.…”

Source and maintenance of the argon atmospheres of Mercury and the Moon

“…The two-path diffusion equations (Lee and Aldama, 1992) are (1) to 275 K is extremely uncertain. However, we are certain that 10-19 em?…”

“…We have used a multipath diffusion code (Lee and Aldama, 1992) to numerically calculate the diffusion of argon from the rocks in which it is created. This multipath diffusion code was written to solve the diffusion equations for a system in which two diffusion paths with different diffusion rates are possible, with an exchange between the two.…”

40Ar/39Ar dating of hydrothermal activity, biota and gold mineralization in the Rhynie hot-spring system, Aberdeenshire, Scotland

“…Models were derived from a modified FOR-TRAN program to solve the diffusion equation originally based on Lee and Aldama (1992) which involved solving two coupled diffusion equations describing the simultaneous diffusion of a chemical species through two different mechanisms (e.g., via volume diffusion through the crystal lattice and short-circuit diffusion through extended defects). The modified program only solves the volume-diffusion equation (i.e., no exchange or coupling with other mechanisms), includes a radioactive source term to account for the production of 40 Ar * over time, and has the ability to use a variable temperature-time history to accurately model any kind of thermal effect throughout the geological history of the rock or mineral.…”

“…The diffusion equation was discretized using a h-method/central-difference scheme (Lee and Aldama, 1992) and all model runs utilized a fully implicit (h = 1) finitedifference solution. K-feldspar crystals of both 1 and 0.1 mm diameter (effective diffusion radii a = 0.5 and 0.05 mm, respectively, data from TEM images [ Fig.…”