A view of Pangong Lake in the Ladakh region of northern India, taken at an altitude of 18,000 feet, shows the great expanse of the Tibetan Plateau extending high and flat in the background, as far as the eye can see. (Photo by P. Clift, Woods Hole Oceanographic Institution)
UNIVERSITY PARK, Pa. The growth of high topography on the Tibetan Plateau in Sichuan, China, began much earlier than previously thought, according to an international team of geologists who looked at mountain ranges along the eastern edge of the plateau. The Indian tectonic plate began its collision with Asia between 55 and 50 million years ago, but "significant topographic relief existed adjacent to the Sichuan Basin prior to the Indo-Asian collision," the researchers report online. "Most researchers have thought that high topography in eastern Tibet developed during the past 10 to 15 million years, as deep crust beneath the central Tibetan Plateau flowed to the plateau margin, thickening the Earth's crust in this area and causing surface uplift," said Eric Kirby, associate professor of geoscience, Penn State. "Our study suggests that high topography began to develop as early as 30 million years ago, and perhaps was present even earlier." Kirby, working with Erchie Wang, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, and Kevin Furlong, professor of geosciences, Penn State, and colleagues from Waikato University, New Zealand and Arizona State University, looked at samples taken from the hanging wall of the Yingxiu-Beichuan fault, the primary fault responsible for the 2008, Wenchuan earthquake. The researchers used a variety of methods including the decay rate of uranium and thorium to helium in the minerals apatite and zircon and fission track dating, an analysis of tracks or trails left by decaying uranium in minerals again in apatite and zircon.
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