THE `STRONG and brittle' theory suggests continents break into pieces during collisions of the tectonic plates, pieces of the Earth's crust into which the continents are embedded. The `weak and viscous' theory suggests, on the contrary, that continents thicken and flow upon collision. Eric Calais, an associate professor of geophysics at Purdue University, in collaboration with Ming Wang and Zenghang Shen from the Institute for Geology and Earthquake Science in China, used global positioning systems to record the precise movements of hundreds of points on the continent of Asia over a 10-year period.
Refining current models
Their new research findings may help refine the accepted models used by earth scientists over the past 30 years to describe the ways in which continents clash to form the Earth's landscape.
Calais said: "With this work, we addressed a fundamental question that geologists have been debating for the past 40 years: Are continents strong and brittle or weak and viscous?"
The data collected by Calais and his teamsuggests the answer is a combination of both theories.
Different at high places
His team found that the surface of the Asian continent behaves differently in areas of high elevation, such as mountains.
Calais and his team gathered data from geodetic markers, metal pins about the size of a pen, that they placed in some of the most remote areas of the world, according to a Purdue University press release.
They are surveyed for a few days every year by GPS tracking equipment, which is then removed once the data is collected. The tops of the markers have a 1-millimetre-wide dimple that is the actual point tracked by the equipment.
The team tracked changes in height and horizontal movements and compared each site to those surrounding it to determine if the larger area responded to forces as a rigid or malleable segment.
If the movement of sites within an area was consistent with a rigid rotation, it could be confirmed that the area fit the strong and brittle theory.
However, a change in height did not necessarily mean an area fit the weak and viscous theory, Calais said.— Our Bureau
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