Diffusional isotopic exchange across an interlayered marble-schist sequence with an application to Tinos, Cyclades, Greece

Marble-schist contacts are frequently characterized by fine-scale interlayering which prevents the application of semi-infinite layer width assumptions to advection/diffusion models of isotope profiles. Using a finite layer width boundary condition, we show that the minimum width (w) of a layer required in order that diffusional exchange at both boundaries will not mutually interfere is given by the relation w > κ (Dt)^1/2, where D is the effective diffusion coefficient, t is the duration of the diffusion and κ is a constant determined by the initial compositional step and the noise (i.e., natural homogeneity and/or analytical accuracy). When this condition is not satisfied, a solution of the diffusion equation for a multilayer transition zone containing several schist and marble layers of different, finite, widths is applicable. Application of this refinement of the diffusion model to an oxygen isotope profile from Tinos (Cyclades) Greece gives 10^-4 ≤ Dt ≤ 10^-2 m². -from Authors