U–Pb geochronology of two augen gneiss terranes, Idaho—new data and tectonic implications

Karl V. Evans; Lynn B. Fischer

doi:10.1139/e86-179

journal article Dec 01, 1986

U–Pb geochronology of two augen gneiss terranes, Idaho—new data and tectonic implications

Karl V. Evans Lynn B. Fischer

Canadian Journal of Earth Sciences Vol. 23 No. 12 pp. 1919-1927 · Canadian Science Publishing

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Abstract

U–Pb isotopic analyses of cogenetic zircon suites revise the ages of two augen gneiss terranes in central and northern Idaho. The augen gneiss of Priest River yields an upper-intercept concordia age for only moderately discordant zircons of 1576 ± 13 Ma; there is no evidence of an inherited xenocrystic lead component. Because this unit probably is in basement beneath Belt–Purcell strata, it provides a maximum age for Belt and Purcell sedimentation. However, high-grade metamorphism and structural complexity permit several tectonic interpretations, all of which should be treated with caution pending further detailed studies.Zircons from the augen gneiss of Red River contain inherited radiogenic lead, but by analogy with lithologically and isotopically similar augen gneiss and porphyritic granite near Salmon and Shoup, Idaho, an age of about 1370 Ma is suggested. However, the uncertainty associated with this value is unknown and could be large. Intrusion preceded or was synkinematic with at least part of the deformation and metamorphism that affected the metasedimentary host rocks, thought by some to be Belt–Purcell strata.

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[1]

Peterman (1968)

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Published: Dec 01, 1986
Vol/Issue: 23(12)
Pages: 1919-1927
License: View

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Cite This Article

Karl V. Evans, Lynn B. Fischer (1986). U–Pb geochronology of two augen gneiss terranes, Idaho—new data and tectonic implications. Canadian Journal of Earth Sciences, 23(12), 1919-1927. https://doi.org/10.1139/e86-179

U–Pb geochronology of two augen gneiss terranes, Idaho—new data and tectonic implications

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