A team of international researchers, led by Monash University’s Dr Wouter Schellart has developed a new global theory of Earth dynamics that explains the motions of the tectonic plates that cover the Earth’s surface and the boundaries between these plates. The new theory has implications for how scientists explain the geological evolution of western North America, including parts of Canada, the USA and Mexico.
The research is published this month in the prestigious journal Science.
“The Earth’s surface is covered with tectonic plates that move with respect to one another at centimetres per year. These plates converge at deep-sea trenches, plate boundaries where one plate sinks (subducts) below the other at so-called subduction zones. The velocities of these plates and the velocities of the boundaries between these plates vary significantly on Earth,” Dr Schellart said.
The research team included Assistant Professor Dave Stegman from Scripps Institution of Oceanography in California, Professor Louis Moresi from Monash University’s Schools of Geology and Mathematical Sciences, and also from Monash University’s School of Mathematical Sciences, Ms Rebecca Farrington and Dr Justin Freeman.
They used observational data and advanced computer models to develop a new mathematical scaling theory, which demonstrates that the velocities of the plates and the plate boundaries depend on the size of subduction zones and the presence of subduction zone edges.
The discovery explains why the Australian, Nazca and Pacific plates move up to four times faster than the African, Eurasian and Juan de Fuca plates.
“It also provides explanations for the motions of the ancient Farallon plate that sank into the mantle below North and South America. This plate slowed down during eastward motion from about 10 centimetres per year some 50 million years ago to only 2 centimetres per year at present.”
The decrease in plate velocity resulted form the decrease in subduction zone size, which decreased from 14000 km to only 1400 km.
“This had a dramatic effect on the topography and the structure of the North American continent. Until approximately 50 million years ago, the west coast of North America was characterized by a massive mountain chain similar to the present day Andes in South America, and ran from Canada in the north to southern Mexico in the south,” Dr Schellart said.
As the subduction zone decreased in size, the compressive stresses along the west coast of North America decreased, resulting in destruction of the mountain range and formation of the Basin and Range province, approximately a 2 million square km area of elongated basins and ridges that characterizes the present-day western North American landscape.
“The new theory provides scientists a dynamic framework in which to interpret the velocities of the tectonic plates in the geological past. It also provides new understanding as to why some subduction zones create massive mountain ranges, such as the Andes in South America, and why others might subsequently destroy their mountain ranges, replacing them with basins and ridges such as in North America, or deep ocean basins such as in the Tasman Sea region to the east of Australia.”
For more information, a copy of the paper or to arrange an interview with Dr Wouter Schellart, contact Samantha Blair, Media and Communications + 61 3 9903 4841 or 0439 013 951.
