3. 96 Ga zircons from an Archean quartzite, Beartooth Mountains, Montana

Journal Article · Wed Apr 01 04:00:00 EST 1992 · Geology; (United States)

DOI:https://doi.org/10.1130/0091-7613(1992)020<0327:GZFAAQ>2.3.CO;2· OSTI ID:7031716

Mueller, P A ^[1]; Wooden, J L ^[2]; Nutman, A P ^[3]

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1. Univ. of Florida, Gainesville (United States)
2. Geological Survey, Menlo Park, CA (United States)
3. Australian National Univ., Canberra (Australia)

U-Pb isotopic systematics of detrital zircons incorporated in a middle Archean quartzite from the Beartooth Mountains, Montana, were investigated with the SHRIMP ion microprobe. These new data reveal an extended and previously unrecognized record of crustal evolution for the northern Wyoming province. Seventy-eight analyses of 67 grains yielded a range of {sup 207}Pb/{sup 206}Pb ages from 2.69 to 3.96 Ga. Concordant analyses from 43 separate grains defined a maximum age for the deposition of the quartzite of 3.30 Ga; other provenance ages extend to 3.96 Ga. Ages of < 3.30 Ga are generally discordant, and appear to reflect late Archean disturbance of the U-Pb system, including metamorphism at {approximately}2.8 Ga. The predominance of ages at {approximately}3.3 Ga is interpreted to represent the last major episode of crust formation prior to deposition of the quartzite. The concordant analyses of > 3.30 Ga indicate that older crustal components with ages up to 3.96 Ga, or detritus from them, were also in the provenance of this quartzite. This older age is equivalent to that of the oldest known rock from the Acasta gneisses of the Slave province and is exceeded only by the > 4.0 Ga age of detrital zircons of the Yilgarn block of Western Australia. These data support an increased probability for the survival of sialic crust created before the cessation of the late bombardment at 3.8 to 3.9 Ga.

• OSTI ID: 7031716
• Journal Information: Geology; (United States), Journal Name: Geology; (United States) Vol. 20:4; ISSN GLGYB; ISSN 0091-7613
• Country of Publication: United States
• Language: English

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