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While it is generally assumed that global plate motions are driven by the pattern of convection in the Earth's mantle, the details of that linkage remain obscure. Bouyancy forces associated with subduction of cool, dense lithosphere at zones of plate convergence are thought to provide significant driving force, but the relative magnitudes of other driving and resisting forces are less clear. The ability to consider past as well as present plate motions provides significant additional constraints, because changes in plate motion are necessarily driven by changes in one or more driving or resisting forces, which may be inferred from independent data. Here we first exploit the capabilities of global tectonic models focused on the Andean region to infer plate motion changes as far back as Miocene time.
By accurately predicting observed convergence rates between Nazca and South America plates over the last 10 m.y., we demonstrate for the first time that the topographic load of the Andes increases resisting forces between downgoing and overriding plates and thus consumes a significant amount of the driving force available for plate tectonics. Such result suggests a strong feedback between mountain belt growth and plate convergence. Moreover, we show that histories of spreading for Nazca/Pacific, Nazca/Antarctica as well as for South America/Africa plates over the past 10 m.y. can be entirely explained through the sole effect of Andean growth on the kinematics of Nazca and South America plates. By affecting relative plate motion changes in South Atlantic and South Pacific, resisting forces related to Andean growth drive about 20% of the global plate motion changes over the past 10 m.y.
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