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Garnet–monazite rare earth element relationships in sub-solidus metapelites: a case study from Bhutan

Warren, Clare J.; Greenwood, Lucy V.; Argles, Tom W.; Roberts, Nick M.W.; Parrish, Randall R.; Harris, Nigel B.W.. 2019 Garnet–monazite rare earth element relationships in sub-solidus metapelites: a case study from Bhutan. In: Ferrero, S., (ed.) Metamorphic geology: microscale to mountain belts. London, UK, Geological Society of London, 145-166. (Geological Society Special Publications, 478, 478).

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Abstract/Summary

A key aim of modern metamorphic geochronology is to constrain precise and accurate rates and timescales of tectonic processes. One promising approach in amphibolite and granulite-facies rocks links the geochronological information recorded in zoned accessory phases such as monazite to the pressure–temperature information recorded in zoned major rock-forming minerals such as garnet. Both phases incorporate rare earth elements (REE) as they crystallize and their equilibrium partitioning behaviour potentially provides a useful way of linking time to temperature. We report REE data from sub-solidus amphibolite-facies metapelites from Bhutan, where overlapping ages, inclusion relationships and Gd/Lu ratios suggest that garnet and monazite co-crystallized. The garnet–monazite REE relationships in these samples show a steeper pattern across the heavy (H)REE than previously reported. The difference between our dataset and the previously reported data may be due to a temperature-dependence on the partition coefficients, disequilibrium in either dataset, differences in monazite chemistry or the presence or absence of a third phase that competed for the available REE during growth. We urge caution against using empirically-derived partition coefficients from natural samples as evidence for, or against, equilibrium of REE-bearing phases until monazite–garnet partitioning behaviour is better constrained.

Item Type: Publication - Book Section
Digital Object Identifier (DOI): https://doi.org/10.1144/SP478.1
ISSN: 0305-8719
NORA Subject Terms: Earth Sciences
Date made live: 26 Jul 2018 15:15 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/520555

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