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Quartz-albite rocks of ash-fall origin

Published online by Cambridge University Press:  01 May 2009

Evan C. Leitch
Evan C. Leitch
Affiliation:
Department of Geology and Geophysics, University of Sydney, N.S.W. 2006, Australia
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Summary

Thin beds composed mainly of quartz and albite occur interstratified with epiclastic rocks in a thick marine Early Permian sequence in the eastern part of the New England Fold Belt, eastern Australia. The sequence has suffered very low grade regional metamorphism and the quartz-albite rocks retain few primary textural features. A pyroclastic origin for these rocks is argued on the basis of inherited sedimentary characters and their distinctive mineralogical and chemical composition, and it is suggested that they accumulated as glass-rich ash-fall tuffs. The present chemical composition of the quartz-albite rocks suggests the tuffs may have initially altered to zeolitic assemblages. Similar quartz-albite rocks, perhaps misidentified as chert or siliceous siltstone, probably occur in other low-grade metamorphic sequences, the progenitors of which accumulated adjacent to active magmatic arcs.

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Type
Articles
Information
Geological Magazine , Volume 118 , Issue 1 , January 1981, pp. 83 - 88
Copyright
Copyright © Cambridge University Press 1981

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