Age trends in garnet-hosted monazite inclusions from upper amphibolite facies schist in the northern Grouse Creek Mountains, Utah

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doi: 10.1016/j.gca.2008.08.012
Authors:Hoisch, Thomas D.; Wells, M. L.; Grove, M.
Author Affiliations:Primary:
Northern Arizona University, Department of Geology, Flagstaff, AZ, United States
Other:
University of Nevada at Las Vegas, United States
University of California, Los Angeles, United States
Volume Title:Geochimica et Cosmochimica Acta
Source:Geochimica et Cosmochimica Acta, 72(22), p.5505-5520. Publisher: Elsevier, New York, NY, International. ISSN: 0016-7037
Publication Date:2008
Note:In English. Includes appendices. 84 refs.; illus., incl. 1 table, geol. sketch map
Summary:We performed in situ Th-Pb dating of monazite in upper amphibolite facies pelitic schist from the Grouse Creek Mountains in northwest Utah. Sixty-six ages from inclusions in four garnet grains range from 37 to 72 Ma and decrease with radial distance from garnet cores. The age range of 30 matrix monazite grains overlaps and extends to younger ages than inclusions (25-58 Ma). The monazite grains are not intersected by cracks in the garnets, through which dissolution, reprecipitation or Pb loss might occur, and are generally too small (<20 µm) to allow for more than one age determination on any one grain. Processes that might explain inclusion ages that decrease with radial distance from garnet cores include: (1) Pb diffusion in monazite, (2) dissolution and reprecipitation of monazite, and (3) co-crystallization of monazite and garnet. After consideration of these possibilities, it is concluded that the co-crystallization of monazite and garnet is the most plausible, with monazite neoblasts deriving REEs from the breakdown of muscovite. Garnet ages derived by regression of the inclusion ages and assuming a constant rate of volume increase during garnet growth yield model ages with a maximum difference between core and rim of 22 m.y. Abstract Copyright (2008) Elsevier, B.V. [R.K.H.]
Sections:Age determination
Subsections:Non-silicates
Subjects:Absolute age; Amphibolite facies; Cenozoic; Chemical composition; Crystal chemistry; Crystallization; Dates; Eocene; Facies; Garnet group; Geochemistry; Inclusions; Metals; Metamorphic rocks; Mineral assemblages; Miocene; Monazite; Neogene; Nesosilicates; Orthosilicates; Paleogene; Pb/Th; Petrography; Phosphates; Rare earths; Silicates; Statistical distribution; Tertiary; Textures; Trace elements; Box Elder County Utah; United States; Utah; Grouse Creek Mountains
Coordinates:N413500 N420000 W1134000 W1135000
Abstract Numbers:08M/4203
Record ID:2009030884
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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