‘Boomerang’ migratory intraplate Cenozoic volcanism, eastern Australian rift margins and the Indian-Pacific mantle boundary
F. L. SUTHERLAND, 2003. "‘Boomerang’ migratory intraplate Cenozoic volcanism, eastern Australian rift margins and the Indian-Pacific mantle boundary", Evolution and Dynamics of the Australian Plate, R.R. Hillis, R.D. Müller
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East Australian and Tasman Sea volcanism has featured in Australian Plate dynamics since Tasman Sea – Coral Sea formation from 95 to 55 Ma. Migratory southward plume-related volcanism, the East Australian Plume System, was prominent after 35 Ma, but new studies reveal unusual features. ‘Swell and pinch’ episodes produced large central volcanoes in initial west-directed ‘swells’ followed by smaller volume fields in easterly ‘pinches’ in late activity. These episodes (‘boomerangs’) each lasted over 10–20 million years, as sidestepping bursts along four main plume lines. The Tasmantid submarine volcanic line shows a westerly ‘swell’ in concert with that in a major Queensland line. Reconstruction of Australian palaeoplate motions from the present dormant plume array match times of ‘swell and pinch’ activity, but not its bending. Each episode includes a less curved, precursory migratory line, erupted some 3 million years before the main migratory line. Plume lines projected back beyond 40 Ma give increasingly divergent plate paths depending on use of a Pacific or Indian hot-spot frame. Averaged plate paths coincide with Coral Sea- Louisiade spreading at 60 Ma, suggesting its potential role in originating the plume array. Precursor and main ‘boomerang’ activity may arise from separate initial plume pulses: lesser rift-related pulse followed by a stronger spreading-related pulse. An alternative possibility is a dual line plume progression caused by transfer of activity through loading and flexure. The west-bending ‘swells’ appear to reflect plume deflection during plume surges. Isotopic Sr, Nd and Pb relationships between East Australian Plume System and other Australian basalts suggest the plume array straddles the Indian and Pacific mantle domain boundary. Replacement of wedges of Indian-type mantle by Pacific-type mantle during northerly Australian Plate translation may focus dynamic flow vectors that contribute to west-bending ‘boomerang’ migratory volcanism.