posted on 2023-05-26, 23:53authored byHajitaheri, J
The Heemskirk Granite intruded Precambrian and Cambrian rocks in western Tasmania in the Devonian. It congists of red and white granite types with the texture in both granite types ranging from porphyritic to equigranular. The white granite underlies and intrudes into the red types. The two types are similar mineralogically and chemically and, apart from the colour difference, the white has more miarolitic cavities, more alteration and a higher tourmaline content than the red granite. The red granite consists of shallow-dipping layers, each of which intruded and chilled against an upper preexisting layer. The layering in the white granite is only localised and the grainsize gradually increases away from the contact with the red granite. The combined thickness of the red layers is about 300m while the white granite is at least 500m thick. It is postulated that the Heemskirk Granite grew by intrusion of sheets into space formed by subsidence within a cauldron-type structure. The granite mainly consists of quartz, feldspar and biotite. Hornblende is only present locally in porphyritic red granite. It is pervasively altered with at least three generations of albite and biotite and two generations of quartz and chlorite. Biotite compositional differences between the two granite types may result from reequilibration of biotite to lower temperatures in the white granite.
Copyright 1985 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Thesis (Ph.D.)--University of Tasmania, 1986. 1 folded map in pocket. Bibliography: leaves [248b]-272