| Abstract: | The only reliable method for dating kimberlites at present is the lengthy and specialized hydrothermal procedure that extracts 206Pb and 238U from low-uranium zircons. This paper describes a second successful method by fission track dating of large single-crystal zircons, 1.0-1.5 cm in dimension. The use of large crystals overcomes the limitations imposed in conventional fission track analysis which utilizes crushed fragments. Low track densities, optical track dispersion, and the random orientation of polished surfaces in the etch and irradiation cycle are effectively overcome. Fission track ages of zircons from five African kimberlites are reported, from the Kimberley Pool (90.3 ?? 6.5 m.y.), Orapa (87.4 ?? 5.7 and 92.4 ?? 6.1 m.y.), Nzega (51.1 ?? 3.8 m.y.), Koffiefontein (90.0 ?? 8.2 m.y.), and Val do Queve (133.4 ?? 11.5 m.y.). In addition we report the first radiometric ages (707.9 ?? 59.6 and 705.5 ?? 61.0 m.y.) of crustal zircons from kimberlites in northwest Liberia. The fission track ages agree well with earlier age estimates. Most of the zircons examined in this study are zoned with respect to uranium but linear correlations are established (by regression analysis) between zones of variable uranium content, and within zones of constant uranium content (by analysis of variance). Concordance between the fission track method and the U/Pb technique is established and we concluded that track fading from thermal annealing has not taken place. Kimberlitic zircons dated in this study, therefore, record the time of eruption. ?? 1983. |
| Genre: | Article |
| ProdID: | 70011443 |
| Citation Author: | Haggerty, S. E.; Raber, E.; Naeser, C. W. |
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| Citation End Page: | 50 |
| Citation Issue: | 1 |
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| Citation Language: | English |
| Citation Larger Work Title: | Earth and Planetary Science Letters |
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| Citation Number Of Pages: | 10 |
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| Citation Search Results Text: | Fission track dating of kimberlitic zircons; 1983; Article; Journal; Earth and Planetary Science Letters; Haggerty, S. E.; Raber, E.; Naeser, C. W. |
| Citation Start Page: | 41 |
| Citation Volume: | 63 |
| Citation Year: | 1983 |
| Type: | citation/reference |
| Text: | Fission track dating of kimberlitic zircons; 1983; Article; Journal; Earth and Planetary Science Letters; Haggerty, S. E.; Raber, E.; Naeser, C. W. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| Date Other: | Sat, 1 Jan 1983 00:00 -0600 |
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