Abstract

The Nychum Volcanics, which were emplaced on the continental side of the Tasman Geosyncline immediately after the mid-Carboniferous orogeny, are composed mostly of acid pyroclastics and lavas, together with subordinate andesite and minor basalt. They are intruded by closely associated plugs of andesite and rhyolite, and a dyke swarm. The volcanics show calc-alkaline characteristics, except for two andesites that have tholeiite-like mineralogy and major-element chemistry. It is suggested that the volcanics are derived from three magma types, and have been affected by both high-pressure and low-pressure fractionation.

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