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Age mapping and dating of monazite on the electron microprobe: Deconvoluting multistage tectonic histories
Geology (1999)
  • ML Williams, University of Massachusetts - Amherst
  • MJ Jercinovic
  • MP Terry
Abstract
High-resolution X-ray mapping and dating of monazite on the electron microprobe are powerful geochronological tools for structural, metamorphic, and tectonic analysis. X-ray maps commonly show complex Th, U, and Pb zoning that reflects monazite growth and overgrowth events. Age maps constructed from the X-ray maps simplify the zoning and highlight age domains. Microprobe dating offers a rapid, in situ method for estimating ages of mapped domains. Application of these techniques has placed new constraints on the tectonic history of three areas. In western Canada, age mapping has revealed multiphase monazite, with older cores and younger rims, included in syntectonic garnet. Microprobe ages show that tectonism occurred ca. 1.9 Ga, 700 m.y. later than mylonitization in the adjacent Snowbird tectonic zone. In New Mexico, age mapping and dating show that the dominant fabric and triple-point metamorphism occurred during a 1.4 Ga reactivation, not during the 1.7 Ga Yavapai-Mazatzal orogeny. In Norway, monazite inclusions in garnet constrain high-pressure metamorphism to ca. 405 Ma, and older cores indicate a previously unrecognized component of ca. 1.0 Ga monazite. In all three areas, microprobe dating and age mapping have provided a critical textural context for geochronologic data and a better understanding of the complex age spectra of these multistage orogenic belts.
Disciplines
Publication Date
January 1, 1999
Publisher Statement
Doi: 10.1130/0091-7613(1999)027<1023:AMADOM>2.3.CO;2
Citation Information
ML Williams, MJ Jercinovic and MP Terry. "Age mapping and dating of monazite on the electron microprobe: Deconvoluting multistage tectonic histories" Geology Vol. 27 Iss. 11 (1999)
Available at: http://works.bepress.com/michael_williams/75/