Electron microprobe dating of monazite

Abstract: The age and composition of monazite from ortho- and paragneisses of the Nizke Tatry Mts Low Tatra Mts was studied by microprobe chemical method. The monazite shows relatively uniform composition characterized by substitutions to xenotime 7—10 mol. Biotite-hosted monazite is commonly overgrown by thin REE-epidote rims, in a less foliated sample it is apparently unstable and breaks down to apatite, REE-epidote and a Th-silicate huttonite? Empirical thermometers based on Y in monazite give —? C for xenotime-bearing samples.

Monazite RW-1: a homogenous natural reference material for SIMS U–Pb and Th–Pb isotopic analysis

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Monazite is a light rare earth element LREE -bearing phosphate mineral. Crystals typically contain distinct chemical domains, each of which represent successive growth thru geologic history. Electron microprobe analysis can characterize the geometry and U-Th- total Pb age for each domain. This kind of data allow the growth of monazite to be related to geologic events affecting the host rock. Monazite is common in pelitic and psammitic metamorphic rocks at greenschist facies and above where it is often recognized as inclusions in porphyroblasts but may also be in direct connection with the matrix. Locating monazite grains can be done on standard geological thin sections via x-ray compositional mapping. Figure 7A reveals a cerium x-ray map on a quartzite sample from the Cheyenne belt.

Monazite geochronology

Electron microprobe analysis of U, Th, and Pb in naturally occurring minerals can indicate their age. Where the Pb is entirely due to the radioactive decay of U and Th, the time since mineral formation or equilibration can be calculated. Any stable U- or Th-bearing phase can be considered. Careful analysis is required with attention to interferences, background measurement, detection limits, and Pb-free sample preparation. Ages can be determined from uraninite older than 2 Ma for a Pb detection limit of 0.
All publications more feeds DOI: BibTeX file. Electron microprobe dating of monazite was performed on enclaves of sapphirine-bearing granulites and their host granites from the southeastern part of the Madurai Block in India. The granulites are strongly migmatitic and comprise quartzofeldspathic leucosome veins and restitic domains of sapphirine, garnet, orthopyroxene, sillimanite and cordierite.
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