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The AAPG/Datapages Combined Publications Database

Journal of Sedimentary Research (SEPM)

Abstract


Journal of Sedimentary Petrology
Vol. 57 (1987)No. 4. (July), Pages 630-638

Provenance Determination of Volcaniclastic Rocks: the Nature and Tectonic Significance of a Cambrian Conglomerate from the New England Fold Belt, Eastern Australia

Evan C. Leitch, Peter A. Cawood (2)

ABSTRACT

The Murrawong Creek and Pipeclay Creek Formations of the New England Fold Belt of eastern Australia provide one of the few records of Middle Cambrian-(?) Early Ordovician sedimentation along the eastern Gondwana margin. They comprise conglomerate, sandstone, siltstone, and laminated argillite that accumulated in an inner-submarine-fan environment. Sandstones are quartz-poor volcanolithic varieties. Conglomerate clasts are mainly andesite but range from basalt to rhyolite; all these rocks are porphyritic with phenocrysts of feldspar (albite after calcic plagioclase), augite, and, uncommonly, titanomagnetite. The augite is a low-TiO2 variety, and titanomagnetite has only a modest TiO2 content. Alteration has modified the magmatic composition of the clasts, but the ess mobile elements indicate they were derived from a low-K orogenic suite, in consonance with petrographic and mineralogical data. A western source and the presence of lower Paleozoic subduction-complex rocks to the east of the Cambrian-(?) Ordovician units indicates that the latter accumulated in a forearc setting. The distributive province may have been the precursor of the Macquarie Volcanic Belt of the eastern Lachlan Fold Belt in N.S.W., or one of the Cambrian oceanic island arcs preserved in the fragmented Gondwana margin sequences in southeastern Australia, northern Victoria Land (Antarctica), and New Zealand.


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