Experimental alteration of monazite in granitic melt: variable U–Th–Pb and REE mobility during melt-mediated coupled dissolution-precipitation

Jan Varga*, Tom Raimondo, Nathan R. Daczko, John Adam

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)

Abstract

Monazite U–Th–Pb geochronology of high-temperature and melt-bearing metamorphic rocks sometimes produces a continuum of concordant ages (‘smear’) without well-defined age populations. In combination with textural and geochemical criteria, these datasets are typically interpreted to infer either variable Pb-loss between two discrete events or protracted metamorphism lasting >50 Myr. We experimentally react monazite with granitic melt (0.7 GPa and 750 °C) to produce a range of complex monazite textures and age patterns similar to those found in natural high-temperature rock samples. Our observations show that within a short duration (≤24 h experiment time), variable REE, Y, Th, U and Pb mobility is achieved via coupled dissolution-precipitation in a melt-bearing system. An ultra-local interface melt is saturated in dissolved components, including the U–Th–Pb isotopic character of the original monazite, such that newly precipitated monazite may copy or partly inherit the age of a precursor grain. This implies that monazite grown via coupled dissolution-precipitation may not faithfully record the age or duration of metamorphism in melt-bearing rocks typical of a variety of geodynamic settings.

Original languageEnglish
Article number119602
Pages (from-to)1-16
Number of pages16
JournalChemical Geology
Volume544
DOIs
Publication statusPublished - 30 Jun 2020

Keywords

  • Monazite
  • Experimental petrology
  • U–Th–Pb
  • Coupled dissolution-precipitation
  • Metamorphism

Fingerprint Dive into the research topics of 'Experimental alteration of monazite in granitic melt: variable U–Th–Pb and REE mobility during melt-mediated coupled dissolution-precipitation'. Together they form a unique fingerprint.

Cite this