| 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 |
| Genre: | Article |
| ProdID: | 70012021 |
| Citation Author: | Peterman, Z. E. |
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| Citation End Page: | 146 |
| Citation Issue: | 3 pt 1 |
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| Citation Language: | English |
| Citation Larger Work Title: | Bulletin of the Geological Society of America |
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| Citation Number Of Pages: | 8 |
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| Citation Publisher: | Geological Society of America |
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| Citation Search Results Text: | Dating of Archean basement in northeastern Wyoming and southern Montana.; 1981; Article; Journal; Bulletin of the Geological Society of America; Peterman, Z. E. |
| Citation Start Page: | 139 |
| Citation Volume: | 92 |
| Citation Year: | 1981 |
| Type: | citation/reference |
| Text: | Dating of Archean basement in northeastern Wyoming and southern Montana.; 1981; Article; Journal; Bulletin of the Geological Society of America; Peterman, Z. E. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| URL (DIGITAL OBJECT IDENTIFIER): | http://dx.doi.org/10.1130/0016-7606(1981)92<139:DOABIN>2.0.CO;2 |
| Date Other: | Thu, 1 Jan 1981 00:00 -0600 |
| Publisher: | Geological Society of America |
