Monazite-xenotime-garnet equilibrium in metapelites and a new monazite-garnet thermometer

Joseph M. Pyle, Frank S. Spear, Roberta L. Rudnick, William F. McDonough

Research output: Contribution to journalArticlepeer-review

313 Citations (Scopus)

Abstract

Prograde suites of pelitic rocks were examined with electron microprobe and laser ablation inductively coupled plasma mass spectrometry to determine the systematics of element partitioning between coexisting monazite, xenotime, and garnet. Monazite grains that grew in equilibrium with xenotime are enriched in γ and Dy compared with monazite that grew in xenotime-absent assemblages. γ and heavy rare earth element contents of monazite coexisting with xenotime increase with rising temperature. Monazite-xenotime γ-Gd and γ-Dy partitioning is systematic within a metamorphic grade, and increases slightly with increasing metamorphic grade, suggesting that monazite-xenotime pairs approached partitioning equilibrium. Garnet and monazite in both xenotime-bearing and xenotime-absent assemblages show a strong (R2 = 0.94) systematic relationship between inverse temperature and In (KFA) for the net-transfer equilibrium γAG + OH-Ap + (25/4) Qtz = (5/4)Grs + (5/4)An + 3γPO4-Mnz + 1/2H2O, suggesting that garnet and monazite crystallized in compositional equilibrium. The following temperature-KFA relationship for the equilibrium above has been derived: T(°C = [-1·45p(bars) + 447772 (± 32052) / 567 (± 40)- Rln (KEq)] - 273·15 with a precision of some ± 30°C for temperature estimates. Our observations suggest that major and accessory phases interact in a coupled fashion during metamorphism, and also approach a state of compositional equilibrium as reactions proceed.

Original languageEnglish
Pages (from-to)2083-2107
Number of pages25
JournalJournal of Petrology
Volume42
Issue number11
DOIs
Publication statusPublished - 2001

Keywords

  • Garnet
  • Monazite
  • Partitioning
  • Thermometry
  • Xenotime

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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