First evidence for Ordovician igneous activity in the dial range trough, Tasmania
作者:
J. B. Jago,
J. A. Cooper,
K. D. Corbett,
期刊:
Journal of the Geological Society of Australia
(Taylor Available online 1977)
卷期:
Volume 24,
issue 1-2
页码: 81-86
ISSN:0016-7614
年代: 1977
DOI:10.1080/00167617708728968
出版商: Taylor & Francis Group
数据来源: Taylor
摘要:
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 initial87Sr/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.
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