The Tibetan Plateau, a land mass nearly the size of the lower half of the United States, was thrust skyward when the Indian and Eurasian tectonic plates collided about 50 million years ago. But existing models of the order of events following the impact may be wrong, according to a recent report.
By claiming that the more northern regions of the plateau formed early in the aftermath, the report contradicts current views, which suggest that crustal contortions and uplift began where continents collided at the southern border of the Eurasian plate and gradually rippled northward.
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In search of hard evidence to test the models, researchers ventured into the Hoh Xil Basin, a northern region of the plateau in China where few dare go because of the snow, high altitude, visas, military headquarters, and other challenges, explains Xixi Zhao, a geophysicist from the University of California, Santa Cruz, who participated in the study.
“Our understanding was driven largely by models that predict that [the plateau] is older in the south and younger in the north,” comments Paul Kapp of the University of Arizona in Tucson. “Then [those researchers] got on the ground and realized the actual land doesn’t match the model.”
Uplift in the central part of the plateau happened before uplift in the south, the team reports in the April 1 Proceedings of the National Academy of Sciences. Fossils of radiolarians, or unicellular marine protozoans, recovered from the Himalayas at the southern border revealed that the mountains must have been underwater 40 million years ago—after the central plateau had already emerged.
These findings aren’t only about dates, Kapp says. “They provide support for a new story on plateau growth, from the inside out.”