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A Cretaceous phonolite dyke from the Tomahawk River, northeast Tasmania

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Everard, JL, 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, vol. 138 , pp. 11-34 , doi: 10.26749/rstpp.138.11.

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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
Authors/Creators:Everard, JL and Sutherland, FL and Zwingmann, H
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
ISSN: 0080-4703
DOI / ID Number: 10.26749/rstpp.138.11
Collections: Royal Society Collection > Papers & Proceedings of the Royal Society of Tasmania
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