Unearthing Past of Tibetan Plateau

Bordered by the Himalayas, the world's highest and largest plateau actually rose in stages instead of all at once, new research shows. These stages occurred at significantly different times, and the center of the plateau rose long before the Himalayas.

While many scientists think that Tibet became a high plateau about 15 million years ago, the U.S. and Chinese geologists found that the center of the plateau rose 40 million years ago, said Xixi Zhao, one of the study's authors at the University of California, Santa Cruz.

Their findings were published in the Proceedings of the National Academy of Sciences (online the week of March 24 and later in print).

Marine fossils suggest that the Himalayas remained below sea level at a time when the central plateau was already at or near its modern elevation, said Zhao, which is an average of 14,850 feet (4,500 meters).

Among other dating techniques, the team used past changes in Earth's magnetic field recorded in the magnetization of the rocks, called magnetostratigraphy. They also discovered volcanic rock in an area of the central plateau. The hardened lava lies on top of tilted and folded layers of sedimentary rocks, and geochronology techniques dated it to 40 million years ago.

The rise of the Tibetan Plateau led to dramatic changes in the climate, both regionally and globally. For climate researchers trying to understand major episodes of global climate change in Earth's past, the timing of the uplift is a crucial piece of information.

"The existence of a high plateau at least 40 million years ago could have important climatic implications," said Peter Lippert, another author of the study and graduate student.

Known as "the roof of the world," the Tibetan Plateau was created by the ongoing collision of tectonic plates as India plows northward into Asia. The U.S. and Chinese geologists based their findings on extensive field studies conducted mostly in a remote interior region of the Tibetan Plateau.

-- LiveScience Staff

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Image Credit: Xixi Zhao, University of California, Santa Cruz