Journal article
U-Pb SHRIMP geochronology and trace-element geochemistry of coesite-bearing zircons, North-East Greenland Caledonides
Special papers (Geological Society of America), Vol.403, pp.23-43
01/01/2006
DOI: 10.1130/2006.2403(02)
Abstract
Obtaining reliable estimates for the timing of eclogite-facies metamorphism is critical to establishing models for the formation
and exhumation of high-pressure and ultrahigh-pressure (UHP) metamorphic terranes in collisional orogens. The presence of
pressure-dependent phases, such as coesite, included in metamorphic zircon is generally regarded as evidence that zircon growth
occurred at UHP conditions and, if dated, should provide the necessary timing information. We report U-Pb sensitive high-resolution
ion microprobe (SHRIMP) ages and trace-element SHRIMP data from coesite-bearing zircon suites formed during UHP metamorphism
in the NorthEast Greenland Caledonides. Kyanite eclogite and quartzofeldspathic host gneiss samples from an island in Jøkelbugt
(78°00′N, 18°04′W) contained subspherical zircons with well-defined domains in cathodoluminescence (CL) images. The presence
of coesite is confirmed by Raman spectroscopy in six zircons from four samples. Additional components of the eclogite-facies
inclusion suite include kyanite, omphacite, garnet, and rutile. The trace-element signatures in core domains reflect modification
of igneous protolith zircon. Rim signatures show flat heavy rare earth element (HREE) patterns that are characteristic of
eclogite-facies zircon. The kyanite eclogites generally lack a Eu anomaly, whereas a negative Eu anomaly persists in all domains
of the host gneiss. The 207 Pb-corrected 206 Pb/ 238 U ages range from 330 to 390 Ma for the host gneiss and 330–370 Ma for the kyanite eclogite. Weighted mean 206 Pb/ 238 U ages for coesite-bearing domains vary from 364 ± 8 Ma for the host gneiss to 350 ± 4 Ma for kyanite eclogite. The combined
U-Pb and REE data interpreted in conjunction with observed CL domains and inclusion suites suggest that (1) Caledonian metamorphic
zircon formed by both new zircon growth and recrystallization, (2) UHP metamorphism occurred near the end of the Caledonian
collision, and (3) the 30–50 m.y. span of ages records long residence times at eclogite-facies conditions for the UHP rocks
of North-East Greenland. This spread in observed ages is interpreted to be characteristic of metamorphic rocks that have experienced
relatively long (longer than 10 m.y.) residence times at UHP conditions.
Details
- Title: Subtitle
- U-Pb SHRIMP geochronology and trace-element geochemistry of coesite-bearing zircons, North-East Greenland Caledonides
- Creators
- William C. McClellandSiobhán E. PowerJane A. GilottiFrank K. MazdabBrigitte Wopenka
- Resource Type
- Journal article
- Publication Details
- Special papers (Geological Society of America), Vol.403, pp.23-43
- Publisher
- Geological Society of America
- DOI
- 10.1130/2006.2403(02)
- ISSN
- 0072-1077
- eISSN
- 2331-219X
- Language
- English
- Date published
- 01/01/2006
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984229307102771
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