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Deformed monazite yields high-temperature tectonic ages

T. M. Erickson, M. A. Pearce, R. J. M. Taylor, N. E. Timms, C. Clark, S. M. Reddy and I. S. Buick
Deformed monazite yields high-temperature tectonic ages
Geology (Boulder) (March 2015) 43 (5): 383-386


The deformation of monazite in the polymetamorphic Sandmata granulite complex in India has been investigated by electron backscattered diffraction and sensitive high-resolution ion microprobe (SHRIMP). Quantitative microstructural analyses document the development of deformation twins in {100}, {001}, and {122} orientations; low-angle (<10 degrees ) boundary development associated with dislocation creep; and the development of new grains due to dynamic recrystallization. These data represent the first quantitative evidence of crystal-plastic deformation of natural monazite. SHRIMP U-Th-Pb analysis shows that the host monazite preserves discordant ages as old as 1666 + or - 28 Ma, along a trend from ca. 1720 Ma to ca. 1000 Ma, with increasingly discordant ages recorded in zones of higher lattice distortion. Domains of recrystallized new grains within the monazite record a tightly clustered concordia age of 970 + or - 14 Ma. This age is interpreted to represent the timing of monazite dynamic recrystallization associated with deformation of the host protolith, and is consistent with partial resetting and Pb loss from domains deforming by dislocation creep. The complex, but systematic, relationship between microstructure and age data in monazite provide the first direct evidence of Pb isotope resetting during deformation. The approach illustrates a new methodology for the dating of deformation events in high-grade metamorphic rocks, which are typically difficult to constrain.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 43
Serial Issue: 5
Title: Deformed monazite yields high-temperature tectonic ages
Affiliation: Curtin University, Department of Applied Geology, Perth, West. Aust., Australia
Pages: 383-386
Published: 20150319
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 28
Accession Number: 2015-039970
Categories: Structural geologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2015134
Illustration Description: illus. incl. geol. sketch map
N24°00'00" - N26°00'00", E72°30'00" - E75°30'00"
Secondary Affiliation: Stellenbosch University, ZAF, South Africa
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201519
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