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Dating of Archean basement in northeastern Wyoming and southern Montana.

Geological Society of America Bulletin

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DOI: 10.1130/0016-7606(1981)92<139:DOABIN>2.0.CO;2

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Abstract

Rb-Sr whole-rock and U-Pb zircon ages of granite and gneiss cores from three deep drill holes extend known occurrences of Archean rocks in the subsurface of NE Wyoming and S Montanta. Rb-Sr and K- Ar mineral ages are discordant and reflect early or middle Proterozoic disturbance. Highly altered rocks occur in a thin zone immediately below the sub-Cambrian unconformity. Samples from a few metres deeper in the basement are much fresher but show the effects of this alteration in filled fractures and thin adjacent alteration haloes. Whole-rock Rb-Sr systems have retaioned a fair degree of integrity in spite of increased susceptibility to modification because of the disturbed mineral systems. Interaction of the rocks with water a few metres below the sub-Cambrian unconformity probably occurred for only a relatively short time. Fractures filled rapidly with secondary minerals such as chlorite, anhydrite, and carbonate to maintain a relatively impermeable crystalline basement in which the silicates and their contained isotopic systems were preserved.- Author

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Dating of Archean basement in northeastern Wyoming and southern Montana.
Series title:
Geological Society of America Bulletin
DOI:
10.1130/0016-7606(1981)92<139:DOABIN>2.0.CO;2
Volume
92
Issue:
3 pt 1
Year Published:
1981
Language:
English
Publisher:
Geological Society of America
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
139
Last page:
146
Number of Pages:
8