No one ever thought the birth of the Rocky Mountains was a simple process, but we now know it was far more complex than even geophysicists had assumed.
New seismic analysis by University of Alberta graduate student Songyun Huang and her supervisor, Jeffrey Gu of the Department of Physics, shows the two plates that formed the mountains were "stacked," with one pushing under the other during the Cretaceous period.
The researchers examined vibrations from earthquakes as they pass through the Earth, creating a high-resolution "snapshot" of the boundaries between the two plates - the Cordilleran layer about 75 km deep, and the craton layer, considered the core of the continent, at 180 km deep. That snapshot reveals a gentle slope of about six degrees dipping westward near the Rocky Mountains, where one plate slid under the other, rather than a sharp vertical step, which had been previously believed.
The study, published last November in Nature Communications, suggests the deep structure continues to evolve today, the bottom of the craton edge appearing to be eroded by the flow of hot mantle rock beneath it.
This stacked architecture is similar to what scientists see beneath the Tibetan Plateau, where the Indian plate is sliding under Asia.
