Origin and Provenance of Submarine Volcaniclastic Rocks in the Late Permian Drake Volcanics, Northeastern New South Wales

Organization: The Australasian Institute of Mining and Metallurgy
Pages: 4
Publication Date: Jan 1, 1987
The Late Permian intermediate to silicic talc-alkaline Drake Volcanics of New England, N.S.W., consist largely of shallow marine, redeposited volcaniclastic rocks which host epithermal Ag-Au deposits. Pervasive hydro- thermal alteration is widespread. The 200-300 m Cataract River Member includes several sedimen- tation cycles composed of massive pumice brec- cias, overlain by laminated sandstones and siltstones, interbedded with marine, fossil- iferous mudstones. Two distinct groups of cla- sts exist within the volcaniclastic beds: 1. Lithics of predominantly intermediate compos- ition lavas that have undergone subaerial epi- clastic erosion and transportation; 2.Pumice, quartz and plagioclase crystals which have not been reworked by epiclastic processes. The lithic clasts were derived locally in a sub- aerial environment within the Drake Volcanics, and pumice and crystal fragments from contem- poraneous centres of silicic volcanism else- where in New England, N.S.W. The latter group of clasts was transported to Drake by Plinian airfall or rafting, and fell and was washed on- to emergent portions of the Drake Volcanics, where reworked locally derived fragments occ- urred. Cold state subaqueous mass-flows, prod- uced by slumping, resedimented the mixed vol- caniclastic detritus into the marine basin in a series of cyclic units with massive lower parts, and laminated upper zones. Modern ana- logs of the palaeogeographic setting in New England, N.S.W., in the Late Permian are pro- vided by the Taupo Zone, New Zealand, and sou- thern Kyushu, Japan.
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