When mountains hit the brakes
Plate tectonics is a widely known theory for explaining the relative motion at Earth’s surface. Unfortunately the driving forces behind plate tectonics are still poorly understood. In particular, the question why direction and speed of individual plate motions change over time, remains unanswered to this date. Recent research at the Ludwig-Maximilians University (LMU) contributes to a more detailed understanding of these forces – by discovering a hitherto unsuspected important player in plate tectonics, as reported in Geology. Giampiero Iaffaldano, a PhD-student, and Professor Hans-Peter Bunge at Geophysics Section of the LMU in collaboration with Timothy H. Dixon at the Rosenstiel School of Marine and Atmospheric Sciences in Miami developed a global computer simulation of Earth’s mantle convection coupled with realistic tectonic plate-models for the surface.
This enabled them for the first time to explain quantitatively the changes in relative motion of the Nazca Plate west of South America over the last ten Million years, that is back into the Miocene era. In their study the researchers employ data from the novel Global Positioning System (GPS). Their results reveal that the approximation of the Nazca and South American Plates slowed by 30 percent over the course of the last ten Million years. Most astonishingly, the computer simulations show that this reduction is linked to increased friction at the plate boundary due to upfolding of the Altiplano Plateau in the central Andes of Bolivia and Peru since the Miocene. In other words, the accumulated weight of the Altiplano, with its height of 6000 meters (approximately 3.7 miles), exorts such pressure on the plate boundary that it effectually functions as a brake on the speed of the Nazca Plate.
This study is the first of its kind where it was possible to successfully “predict” changes in plate motion. Two insights will potentially be of wider consequence. Firstly, the upper 30 kilometers (about 18.6 miles) of Earth’s crust, the so-called brittle part and source-area for many earthquakes, play a larger role in driving plate tectonics than previously assumed. Secondly, a fascinating hypothesis suggests that Earth’s climate exerts direct influence on plate tectonics. In addition to the upfolding, the extreme height of the Altiplano is linked to the arid climate of the region which strongly reduces erosion. So, if on the one hand upfolding of the Altiplano is linked to arid climate, and on the other hand slow-down of the Nazca Plate is linked to the upfolding of the Altiplano, then a possible assumption is that strongly arid climates may influence plate tectionics in mountainous regions. “Understanding the wider impact of consequences of these newly won insights into the inner workings of our planet will be a focus of future studies,” says Iaffaldano.
“Feedback between mountain belt growth and plate convergence”, Giampiero Iaffaldano, Hans-Peter Bunge, Timothy H. Dixon, Geology, October 2006
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