Origin and provenance of submarine volcaniclastic rocks in the Late Permian Drake Volcanics, New South Wales

Abstract

The Late Permian, intermediate to silicic, calc‐alkaline Drake Volcanics of New England, NSW, consist largely of shallow marine, redeposited volcaniclastic rocks, which host epithermal silver‐gold deposits. Pervasive hydrothermal alteration is widespread. The 200–300 m thick Cataract River Member includes several sedimentation cycles composed of massive pumice breccias, overlain by laminated sandstone and siltstone, interbedded with marine, fossiliferous mudstone. Two distinct groups of clasts within the volcaniclastic beds include: (1) lithics of predominantly intermediate‐composition lavas that have undergone subaerial epiclastic erosion and transportation; and (2) pumice, quartz and plagioclase crystals that have not been reworked by epiclastic processes. The lithic clasts were probably derived locally in a subaerial environment within the Drake Volcanics, and pumice and crystal fragments from contemporaneous centres of silicic volcanism elsewhere in New England. The latter group of clasts was transported to Drake by Plinian airfall or rafting, and fell or was washed on to emergent portions of the Drake Volcanics containing reworked locally derived fragments. Cold‐state mass‐flows produced by slumping, redeposited the mixed volcaniclastic detritus into the marine basin in a series of cyclical units with massive lower parts and laminated upper zones. Modern analogues of the palaeogeographic setting in New England in the Late Permian are provided by the Taupo Zone, New Zealand, and southern Kyushu, Japan.

Key words:

• cold‐state mass‐flows
• Drake
• Permian
• submarine volcaniclastic rocks

Notes

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