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| Titel: |
First evidence for Ordovician igneous activity in the dial range trough, Tasmania |
| Auteur: |
Jago, J. B. Cooper, J. A. Corbett, K. D. |
| Verschenen in: |
Australian journal of earth sciences |
| Paginering: | Jaargang 24 (1977) nr. 1-2 pagina's 81-86 |
| Jaar: |
1977-03 |
| Inhoud: |
A small andesitic intrusion, previously considered to be a Middle Cambrian lava, cuts fossiliferous upper Middle Cambrian sediments in the Leven Gorge section of the Dial Range Trough, northwestern Tasmania. Sixteen total-rock samples of this intrusion produce a perfect-fit, rubidium-strontium isochron, which gives an Early Ordo-vician age of 490 ± 18 m.y. for λ87Rb = 1.39 × 10-11y-1, and NBS 70A feldspar = 522 ppm Rb and 65.3 ppm Sr respectively. The initial 87Sr/86Sr ratio of 0.7112 ± 0.0003 suggests a continental type intrusion rather than an island-arc andesite. Rather similar intermediate igneous rocks, at least some of which are intrusive, are common in the Dial Range Trough and could be largely post-Cambrian in age. From the geological time-scale point of view, the only definite information obtained in this work is that the Middle-Late Cambrian boundary is older than the date given above. |
| Uitgever: |
Taylor & Francis |
| Bronbestand: |
Elektronische Wetenschappelijke Tijdschriften |
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