Retentiveness of rare earth elements in garnet with implications for garnet Lu‐Hf chronology
Abstract
Incorporation of rare earth elements (REE) in garnet enables garnet chronology (Sm‐Nd, Lu‐Hf), and imparts a garnet‐stable signature on cogenetic phases, which allows petrochronology and general petrogenetic tracing of garnet stability in minerals and melts. Constraints on the uptake and redistribution mechanisms, as well as on the diffusive behaviour of REE in garnet are required for allowing accurate interpretation of REE signatures and ages. Garnet REE profiles are often measured to gain insight into the nature and cause of REE zoning. Interpretation of such profiles is nevertheless complicated by poor constraints on the extent of diffusive relaxation. This is especially relevant for Lu, which, according to experiments, has a relatively high diffusivity and thus may re‐equilibrate with possible consequences for Lu‐Hf chronology. To provide new insight into the REE systematics of garnet, we applied quantitative trace‐element mapping of garnet grains from metamorphic rocks that record peak temperatures above 750°C and cooling rates as low as 1.5°C Ma −1 . Garnet in all samples preserves Rayleigh‐type or oscillatory growth zoning with sharply defined interfacial angles that match the garnet habit. Re‐equilibration of REE compositions appears restricted to domains with nebulous and patchy zoning, which likely form by interface‐coupled dissolution and re‐precipitation reactions mediated by fluids or melts, rather than REE volume diffusion. The possible effect of Lu diffusion in the analysed grains was investigated by comparing the observations to the results from 2D numerical modelling using Lu diffusivities from recent diffusion experiments. This test indicates that Lu diffuses significantly slower in natural garnet than experiments predict. The retentiveness of REE in garnet demonstrates the reliability of REE signatures in magmatic tracing and petrochronology and establishes Lu‐Hf chronology as a robust means of dating garnet growth and recrystallization in metamorphic rocks, including those that underwent high‐ or ultrahigh‐temperature conditions.
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BibTeX
@article{smit2026retentiveness,
title = {{Retentiveness of rare earth elements in garnet with implications for garnet Lu‐Hf chronology}},
author = {Matthijs A Smit and Johannes C Vrijmoed and Erik E Scherer and Klaus Mezger and Ellen Kooijman and Melanie Schmitt-Kielman and Lorraine Tual and Carl Guilmette and Lothar Ratschbacher},
journal = {Journal of Metamorphic Geology},
year = {2026},
month = oct,
doi = {10.1111/jmg.12769},
url = {https://hal.science/hal-05783888v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Retentiveness of rare earth elements in garnet with implications for garnet Lu‐Hf chronology
AU - Matthijs A Smit
AU - Johannes C Vrijmoed
AU - Erik E Scherer
AU - Klaus Mezger
AU - Ellen Kooijman
AU - Melanie Schmitt-Kielman
AU - Lorraine Tual
AU - Carl Guilmette
AU - Lothar Ratschbacher
PY - 2026
DA - 2026/10/07
JO - Journal of Metamorphic Geology
DO - 10.1111/jmg.12769
UR - https://hal.science/hal-05783888v1
AB - Incorporation of rare earth elements (REE) in garnet enables garnet chronology (Sm‐Nd, Lu‐Hf), and imparts a garnet‐stable signature on cogenetic phases, which allows petrochronology and general petrogenetic tracing of garnet stability in minerals and melts. Constraints on the uptake and redistribution mechanisms, as well as on the diffusive behaviour of REE in garnet are required for allowing accurate interpretation of REE signatures and ages. Garnet REE profiles are often measured to gain insight into the nature and cause of REE zoning. Interpretation of such profiles is nevertheless complicated by poor constraints on the extent of diffusive relaxation. This is especially relevant for Lu, which, according to experiments, has a relatively high diffusivity and thus may re‐equilibrate with possible consequences for Lu‐Hf chronology. To provide new insight into the REE systematics of garnet, we applied quantitative trace‐element mapping of garnet grains from metamorphic rocks that record peak temperatures above 750°C and cooling rates as low as 1.5°C Ma −1 . Garnet in all samples preserves Rayleigh‐type or oscillatory growth zoning with sharply defined interfacial angles that match the garnet habit. Re‐equilibration of REE compositions appears restricted to domains with nebulous and patchy zoning, which likely form by interface‐coupled dissolution and re‐precipitation reactions mediated by fluids or melts, rather than REE volume diffusion. The possible effect of Lu diffusion in the analysed grains was investigated by comparing the observations to the results from 2D numerical modelling using Lu diffusivities from recent diffusion experiments. This test indicates that Lu diffuses significantly slower in natural garnet than experiments predict. The retentiveness of REE in garnet demonstrates the reliability of REE signatures in magmatic tracing and petrochronology and establishes Lu‐Hf chronology as a robust means of dating garnet growth and recrystallization in metamorphic rocks, including those that underwent high‐ or ultrahigh‐temperature conditions.
SN - 0263-4929
SN - 1525-1314
ER -