» Home > In the News

An assumption of Subduction

1 June 2012

Without taking sides this is perhaps an illustration of how science consensus nails the mast down – against all comers. At http://users.indigo.net.au/don/nonsense/subass.html the title is The Convenient Assumption of Subduction and clearly the author favours the expanding earth theory – but the way he presents it makes you think. He begins with a nice image of global subduction zones followed by a quote from the 'Encyclopedia of Structural Geology and Plate Tectonics' (Seyfert) on page 712 … 'if the creation of new oceanic lithosphere at oceanic ridges were the only process operating the Earth clearly would have increased in volume and surface area at a remarkable rate in the comparatively recent geologic past' and later, 'an important element of the seafloor spreading hypothesis from the outset has been the assumption that oceanic lithosphere is being returned to the mantle landward of the deep ocean trenches' and on page 503, 'it is convenient in the context of plate tectonics to emphasise underthrusting (subduction) of one plate rather than overthrusting (overriding) of the other, although kinematically both are equivalent'.

This view is underscored at http://openlearn.open.ac.uk/mod/resource/view.php?id=172177 (2010) and reads, 'the theory of plate tectonics is based on several assumptions. The most important of which are i) new plate material is generated at oceanic ridges or constructive plate boundaries by sea floor spreading, ii) the Earth's surface area is constant and therefore the generation of new plate material must be balanced by the destruction of plate material elsewhere at destructive plate boundaries. Such boundaries are marked by the presence of deep ocean trenches and volcanic island arcs in the oceans and when continental lithosphere is involved, mountain chains, and iii) plates are rigid and can transmit stress over long distances without internal deformation – relative motion between plates is accommodated only at plate boundaries.

The piece then goes on to claim we can't observe subduction – and a lot of plate tectonics is of course done by computer simulation. What geophysicists are really showing is a string of volcanoes – not necessarily a subduction zone. This is the so called Ring of Fire. The author seems to imply geophysicists are somewhat like some of the astro-physicists, long on theory but short on facts. It's an interesting rant – but is the Earth really expanding?

Skip to content