Pb-diffusion in monazite: Constraints from a high-T contact aureole setting

Christopher R.M. McFarlane; T. Mark Harrison

doi:10.1016/j.epsl.2006.06.050

Pb-diffusion in monazite: Constraints from a high-T contact aureole setting

Christopher R.M. McFarlane^*, T. Mark Harrison

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

47 Citations (Scopus)

Abstract

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.

Original language	English
Pages (from-to)	376-384
Number of pages	9
Journal	Earth and Planetary Science Letters
Volume	250
Issue number	1-2
DOIs	https://doi.org/10.1016/j.epsl.2006.06.050
Publication status	Published - 15 Oct 2006

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title = "Pb-diffusion in monazite: Constraints from a high-T contact aureole setting",

abstract = "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.",

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author = "McFarlane, {Christopher R.M.} and {Mark Harrison}, T.",

year = "2006",

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T2 - Constraints from a high-T contact aureole setting

AU - McFarlane, Christopher R.M.

AU - Mark Harrison, T.

PY - 2006/10/15

Y1 - 2006/10/15

N2 - 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.

AB - 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.

KW - Pb diffusion

KW - contact aureole

KW - depth-profiling

KW - monazite

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U2 - 10.1016/j.epsl.2006.06.050

DO - 10.1016/j.epsl.2006.06.050

M3 - Article

SN - 0012-821X

VL - 250

SP - 376

EP - 384

JO - Earth and Planetary Science Letters

JF - Earth and Planetary Science Letters

IS - 1-2

ER -

Pb-diffusion in monazite: Constraints from a high-T contact aureole setting

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