Euler poles for plate motions do not stay fixed in geologic time.
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Geodynamical models and studies of plate reconstructions report that Euler poles for plate motions scatter across geological time rather than remaining fixed.
Terra Nova, 24, 467–476, 2012AbstractA full global, physically coherent geodynamical model over 600 Ma has been developed at the University of Lausanne during the past 20 years, based on the PaleoDyn database, compiling information of geodynamical interest. One of the outstanding results, presented herein, is the distribution of Euler poles (axis around which tectonic plates are moving on the Earth’s surface from one reconstruction to another), which are not randomly distributed, but smeared out along a weakly developed girdle. The scattering reflects the tendency of plates to follow a random evolution. However, the distribution along a preferential plane (‘best‐fitted’ plane) suggests a long‐term influence on plate motion. The fact that the poles predominantly lie within the inter‐tropical zone together with the computed net rotation throughout the Phanerozoic indicating a ‘westward drift’, suggest a long‐term influence of rotational effects.
In the 1960s, geology was transformed by the paradigm of plate tectonics. The 1965 paper of Bullard, Everett and Smith was a linking transition between the theories of continental drift and plate tectonics. They showed, conclusively, that the continents around the Atlantic were once contiguous and that the Atlantic Ocean had grown at rates of a few centimetres per year since the Early Jurassic, about 160 Ma. They achieved fits of the continental margins at the 500 fathom line (approx. 900 m), not the shorelines, by minimizing misfits between conjugate margins and finding axes, poles and angles of rotation, using Euler's theorem, that defined the unique single finite difference rotation that carried congruent continents from contiguity to their present positions, recognizing that the real motion may have been more complex around a number of finite motion poles. Critically, they were concerned only with kinematic reality and were not restricted by considerations of the mechanism by which continents split and oceans grow. Many of the defining features of plate tectonics were explicit or implicit in their reconstructions, such as the torsional rigidity of continents, Euler's theorem, closure of the Tethyan ocean(s), major continental margin shear zones, the rapid rotation of small continental blocks (Iberia) around nearby poles, the consequent opening of small wedge-shaped oceans (Bay of Biscay), and misfit overlaps (deltas and volcanic piles) and underlaps (stretched continental edges). This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society.
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