Provenance ages for metasedimentary rocks from northern Colorado and southern Wyoming: Refinement by U-Pb single-zircon analysis

Conference · Thu Apr 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5022837

Walter, M ^[1]; Ball, T T; Farmer, G L ^[2]

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1. Geological Survey, Denver, CO (United States)
2. Univ. of Colorado, Boulder, CO (United States). Dept. of Geological Sciences

U-Pb ages of single detrital zircons from a paragneiss in the Barber Lake block within the Cheyenne Belt, Medicine Bow Mountains, southeastern Wyoming, and from the quartzite the ages of the sediment-source regions. The paragneiss has been interpreted as metamorphosed, deep oceanic sediments that formed during the accretion of Proterozoic island arcs to the southern margin of the Archean Wyoming craton, a conclusion based on Nd isotopic data from this unit. The zircon data support this interpretation. Of the 19 single crystal analyzed, two gave [sup 207]Pb/[sup 206]Pb ages of 2,539 and 2,466 Ma, respectively, indicating an Archean provenance(s). The remaining 17 crystals gave [sup 207]Pb/[sup 206]Pb ages (minimum ages) ranging from 1,800 to 1,866 Ma, suggesting a provenance of about 1.85 Ga. Previous work on multi-grain zircon samples from the quartzite of Willow Creek yielded [sup 207]Pb/[sup 206]Pb ages of 2,034 and 1,778 Ma. Single-zircon analysis of this sample also shows a Late Archean component along with Early Proterozoic zircons. The Proterozoic zircons can be grouped into three age categories: 1,786-1,750 Ma, 1,893-1,800 Ma, and one, nearly concordant analysis, at 2,092 Ma. Rift-related mafic intrusions in southern Wyoming, as well as Canada, have been dated at 2.1 Ga. The oldest dated rock in Colorado, a metadacite porphyry from the Green Mountain Formation, is 1,792[+-]15 Ma, thus, some of the 1.75 Ga zircons could be derived from northern Colorado.

• OSTI ID: 5022837
• Report Number(s): CONF-9305259--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:5
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AGE ESTIMATION
COLORADO
DEVELOPED COUNTRIES
GEOLOGIC DEPOSITS
GNEISSES
ISOTOPE DATING
ISOTOPES
LEAD ISOTOPES
METAMORPHIC ROCKS
MINERALS
NORTH AMERICA
QUARTZITES
ROCKS
SILICATE MINERALS
USA
WYOMING
ZIRCON