Monday, May 7, 2012

New Thoughts On Subduction


Geologists and many other geographically centered scientists have argued for decades over how the process of plate tectonics had initially evolved.  Recently,  Jeroen van Hunen, a geophysicist at Durham University in England worked with Jean-Fran├žois Moyen, of Jean Monnet University in Saint-Etienne, France to give us their theories.  A model was developed showing how one plate of earth's thin crust subducts below another.
The theory thus far has supported a continuous process where plates converge at boundary points, and are famously based on movement fuelled by temperature and/or substrate mass and density (i.e dense continental crust v. the lighter basaltic rock of oceanic crust).  Some theories in the past have been maintained by evidence of rocks surfaced from mantle regions of the lithosphere and have supported more of a continuous motion of plates at boundaries resulting in subduction (Fig 2.1).

Fig. 2.1 - subduction zone of two plates

photo credit:. Web. 2 May 2012. <volcanoes.usgs.gov>
Moyen and Hunen found rocks striated with pristine rocks layered with altered rock in Zimbabwe and Southern Australia that account for more of a 'start and stop' method of initially forming our modern day plate tectonics.   The discussion follows one of geothermal interest and spotlights convection loops.  The two scientists did their study showing their audiences how changes as few as 200 degrees higher, would cause crust to break off and interrupt the continuous flow theory.  It would take time for the layer to cool enough to begin re-subduction which if anything but a good argument, supports how the ancient rock striations in Zimbabwe have been aligned as they are.

References

Witze, Alexandra. "Stop-and-go plate tectonics." Science News 9 Apr. 2012. Web. 2 May 2012. <http://www.sciencenews.org/view/generic/id/339797/title/Stop-and-go_plate_tectonics>.
Arbogast, Alan F. Discovering Physical Geography. second ed. Hoboken: John Wiley and Sons, 2011. 355-59. Web. 22 Apr. 2012.
Glasscoe, Maggi. History of Plate Tectonics. N.p., n.d. Web. 17 Mar. 2012. <http://scign.jpl.nasa.gov/learn/plate2.htm>.

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