![]() ![]() For South America, this means that the subduction zone bends at the northern and southern ends, as expected. The result is a 'U'-shaped subduction zone.īut with long boundaries, it is too difficult for mantle rock from the middle of the subducting plate to travel all the way around that plate's edges to fill in a gap on the other side, the model finds. It simply nips around the edges, bending them as it does so. When the length of the subduction zone is just a few hundred kilometres long, this flow of replacement rock is easy, the model shows. The upper-mantle material beneath the subducting plate steps in to fill that gap, flowing around the edges of the sinking plate to get there. This leaves a gap on the side of the overriding plate that needs to be filled in with rock. For example, the South American subduction zone, in which the subducting plate is moving eastwards, tries to move westwards over time. The boundary of a sinking plate is known to generally retreat backwards as more and more material slides underground. But longer boundaries - such as the subduction zone off the South American coast, which measures 7,400 kilometres from north to south - move more slowly and develop into a 'W' shape. When subduction zones are short from tip to tail they move relatively quickly, the team found, rapidly adopting a 'U' shape as seen from above. The team was particularly interested in what would happen to the shape of the boundary line between the subducting plate and the overriding one (called the subduction zone) - as seen from a bird's eye view. They plugged in values for the strength and density of our planet's different plates, allowed gravity to pull the denser ones down, and watched what happened. To investigate, Wouter Schellart of the Australian National University in Canberra and colleagues created a computer model of the motion of Earth's tectonic plates over millions of years. Previous calculations based on models of plate tectonics have at times suggested they ought to be half that height. While this 'subduction' process is expected to create mountains through a crumpling of the continental plate above, it's perplexing why the peaks of the central Andes stand at an average height of 4 kilometres. But the Andes were formed where an oceanic plate slides beneath a continent. The highest mountain range on our planet - the Himalayas - was formed by the massive collision of two continental plates. GettyĪ three-dimensional model of our planet's plate tectonics could help to explain why the Andes mountain range is taller than geologists would predict: it could all be down to the long length of the South American continent. These peaks are the result of an unusual plate tectonic crunch. ![]()
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