Dating of Archean basement in northeastern Wyoming and southern Montana.
Geological Society of America Bulletin
By: Z. E. Peterman
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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
| 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 |
| Larger Work Title | Geological Society of America Bulletin |
| First page | 139 |
| Last page | 146 |
| Google Analytic Metrics | Metrics page |