Published on August 17th, 2012 | by Joshua S Hill
Tibetan Plateau May be Older than Previously Thought
The Tibetan Plateau is the planet’s highest and largest plateau and has been the focus of scientific study for decades. In a new study, published online in the journal Nature Geoscience, researchers have discovered that the growth of high topography such as the Tibetan mountains and plateau began much earlier than was previously understood.
“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 at 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 and associates from around the world took samples from the hanging wall of the Yingxiu-Beichuan fault, the primary fault responsible for the 2008, Wenchuan earthquake, and used a variety of dating methods to understand the timeline of the region, and find clues to when specific rocks were lifted.
“These methods allow us to investigate the thermal regime from about 250 degrees Celsius (482 degrees Fahrenheit) to about 60 degrees (140 degrees Fahrenheit),” said Kirby. “The results show that the rocks cooled relatively slowly during the early and mid-Cenozoic — from 30 to 50 million years ago — an indication that topography in the region was undergoing erosion.”
The results of their analyses also suggested that gradual cooling during this time was followed by two episodes of rapid erosion, one which began 30 to 25 million years ago and the second beginning 15 to 10 million years ago that continues through to today.
“These results challenge the idea that the topographic relief along the margin of the plateau developed entirely in the Late Miocene, 5 to 10 million years ago,” said Kirby. “The period of rapid erosion between 25 to 30 million years ago could only be sustained if the mountains were not only present, but actively growing, at this time.”
The researchers also note that this implies that fault systems responsible for the 2008 earthquake were also probably active early in the history of the growth of the Tibetan Plateau.
“We are still a long way from completely understanding when and how high topography in Asia developed in response to India-Asia collision,” notes Kirby. “However, these results lend support to the idea that much of what we see today in the mountains of China may have developed earlier than we previously thought.”
Kirby was joined by Erchie Wang of the Institute of Geology and Geophysics at the Chinese Academy of Sciences in Beijing; Kevin Furlong, professor of geosciences at Penn State; and colleagues from Waikato University, New Zealand and Arizona State University.