Publication Details

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Title: Pb‐diffusion in monazite: Constraints from a high‐T contact aureole setting
Authors: C.R.M. McFarlane, and T.M. Harrison
Publication: Earth Planet. Sci. Lett., v. 250, p. 376‐384.
Publish Date: Oct 2006
DOI: 10.1016/j.epsl.2006.06.050
PDF: pdf
BibTEX Citation: McFarlane:2006.bib


We report measurements of Pb diffusion in natural monazite that was subjected to a static, anhydrous, high‐temperature overprint in the contact aureole of the Makhavinekh Lake Pluton (MLP), northern Labrador, Canada. The 1850 Ma monazite grains we studied were reheated to temperatures of 900 ± 25 °C during intrusion of MLP at 1322 Ma. Ion‐microprobe depth‐profiling reveals the outermost ⁓0.3 µm of these grains to contain Pb/U gradients that can be modeled as a result of one‐dimensional concentration‐independent diffusion (i.e., an error‐function profile) at 1322 Ma. These gradients are combined with temperature‐time histories predicted by a numerical model of conductive heat flow in the contact aureole to calculate Pb diffusion coefficients between 3.2 × 10−28 and 1.3 × 10−27 m2/s. This range overlaps with the down‐temperature extrapolation of experimental Pb diffusion data obtained under dry conditions confirming the slow diffusivity of Pb in monazite at crustal temperatures and timescales.