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A Cretaceous phonolite dyke from the Tomahawk River, northeast Tasmania

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Everard, JL and Sutherland, FL and Zwingmann, H (2004) A Cretaceous phonolite dyke from the Tomahawk River, northeast Tasmania. Papers and Proceedings of the Royal Society of Tasmania, 138. pp. 11-34. ISSN 0080-4703

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Abstract

Field mapping and indicate that a phonolite which intrudes Devonian granite in the upper Tomahawk River
area, Tasmania, is 3.2 km long and with a true thickness of 10-15 m. The rock contains of
anorthoclase, sparse fayalitic olivine and low-Ti and rare biotite in a alkali feldspar laths, with interstitial
clinopyroxene to amphibole or analcime and accessory
apatite. It is peralkaline and evolved, even for phonolites, with very and CaO, and high and
incompatible elements. However, relatively high Sr and Ba and the absence of a negative Eu anomaly suggest little feldspar fractionation
in its petrogenesis. Its Late Cretaceous age 80.4 ± 1.6 Ma, 4oAr/39Ar plateau 75.8 ± 0.3 Ma, 4oAr/39Ar total fusion 76 ± 3.1 Ma) and
geochemistry are unique for Tasmania and it represents a recognised, although very minor, igneous episode. It may be related to a
change in dynamic regime following continental rifting, the opening of the Tasman Sea and the subsidence of Bass Basin.

Item Type: Article
Keywords: Royal Society of Tasmania, RST, Van Diemens Land, natural history, science, ecology, taxonomy, botany, zoology, geology, geography, papers & proceedings, Australia, UTAS Library
Journal or Publication Title: Papers and Proceedings of the Royal Society of Tasmania
Page Range: pp. 11-34
ISSN: 0080-4703
Collections: Royal Society Collection > Papers & Proceedings of the Royal Society of Tasmania
Additional Information:

Copyright Royal Society of Tasmania

Date Deposited: 18 May 2012 02:07
Last Modified: 15 Sep 2017 01:06
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