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Age and nature of the basement in northeastern Washington and northern Idaho: isotopic evidence from Mesozoic and Cenozoic granitoids

Journal of Geology

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Abstract

K-feldspar Pb and whole rock Nd isotopic analyses from 25 Mesozoic and Cenozoic plutonic rocks and two gneisses from NE Washington and northern Idaho are used to elucidate the age and nature of the concealed cratonic basement. The plutons form two highly distinct isotopic groups: Group I have isotopic compositions suggesting derivation from rocks of the Belt Supergroup or their metamorphosed equivalents, Group II have highly retarded Pb isotopic compositions relative to the present day crustal average and require a source region with long-term U depletion, characteristic of cratonic lower crust. A U-Pb zircon upper intercept age of c2600 Ma obtained from one of the Group II samples, together with Sm-Nd data from the gneisses, indicates possible late-Archean crust at depth, which acted as a source region for Eocene extension-related plutonism. -from Authors

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Age and nature of the basement in northeastern Washington and northern Idaho: isotopic evidence from Mesozoic and Cenozoic granitoids
Series title:
Journal of Geology
Volume
100
Issue:
6
Year Published:
1992
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
691
Last page:
701
Number of Pages:
11