He diffusion in monazite: Implications for (U-Th)/He thermochronometry

J. W. Boyce, Kip Hodges, W. J. Olszewski, M. J. Jercinovic

Research output: Contribution to journalArticle

23 Citations (Scopus)

Abstract

The light rare earth phosphate mineral monazite contains high concentrations of Th and U and thus should have potential as a (U-Th)/He thermochronometer. New 4He diffusion experiments confirm this potential but suggest that the bulk closure temperature may be so strongly compositionally dependent that successful applications will require careful sample characterization prior to (U-Th)/He dating. Three experiments were performed on single crystals of Monazite 554, a material that has been used as a standard for Th-Pb ion microprobe geochronology. The data from each experiment yielded a linear array on an Arrhenius diagram, consistent with simple diffusion behavior. However, the diffusion parameters indicated for each grain were statistically different, indicating closure temperatures (assuming a cooling rate of 10°C/ Myr) of 206 ± 24°C, 230 ± 4°C, and 286 ± 13°C. X-ray compositional maps of Monazite 554 illustrate a possible cause of this discrepancy: strong and geometrically complex chemical zoning that varies from grain to grain and likely corresponds to several episodes of growth and dissolution. If He diffusivity in monazite is compositionally controlled, individual crystals with such inconsistent zoning (which is typical of naturally occurring monazites) should have different bulk closure temperatures.

Original languageEnglish (US)
Article numberQ12004
JournalGeochemistry, Geophysics, Geosystems
Volume6
Issue number12
DOIs
StatePublished - Dec 2005
Externally publishedYes

Fingerprint

monazite
closure temperature
closures
Zoning
zoning
geochronology
Phosphate minerals
Geochronology
linear arrays
crystal
dating
diffusivity
temperature
experiment
Experiments
ion microprobe
phosphates
dissolving
rare earth elements
diagrams

Keywords

  • (U-Th)/He
  • Diffusion
  • Monazite
  • Thermochronology

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

Cite this

He diffusion in monazite : Implications for (U-Th)/He thermochronometry. / Boyce, J. W.; Hodges, Kip; Olszewski, W. J.; Jercinovic, M. J.

In: Geochemistry, Geophysics, Geosystems, Vol. 6, No. 12, Q12004, 12.2005.

Research output: Contribution to journalArticle

Boyce, J. W. ; Hodges, Kip ; Olszewski, W. J. ; Jercinovic, M. J. / He diffusion in monazite : Implications for (U-Th)/He thermochronometry. In: Geochemistry, Geophysics, Geosystems. 2005 ; Vol. 6, No. 12.
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