Salt of the Earth (on salt domes and beds)

Sculpting the Earth from Inside Out-Michael Gurnis 2001

Partial Quote:to determine whether downward flow of the mantle could have caused the dip near Denver, (Christopher) Beaumont teamed up with jerry Mitrovica, then a graduate student at the university of Toronto, and Gary T. Jarvis of York University in Toronto. They found that the sinking of North America during the Cretaceous could have been caused by a plate called the Farallon as it plunged into the mantle beneath the western coast of North America. Basing their conclusion on a computer model, the research team argued that the ancient plate thrust into the mantle nearly horizontally. As it began sinking, it created a downward flow in its wake that tugged North America low enough to allow the ocean to rush in. As the Farallon plate sank deeper, the power of its trailing wake decreased. the continent's tendency to float eventually won out. and North America resurfaced.When the Canadian researchers advanced their theory in 1989, The Farollon plate had long since vanished into the mantle, so its existance had only been inferred from geologic indications on the bottom of the Pacific ocean. At that time. no seismic images were of high enough resolution to delineate a structure as small as a sinking fragment of the sea floor. Then, in 1996, new images of the mantle changed everything. Stephan P. Grand of the University of Texas at Austin and Robert D. van der Hilst of M. I. T., seismologists from separate research groups, presented two images based on entirely different sets of seismic measurements. Both pictures showed virtually identical structures, especially the cold-mantle downdwellings associated with the sinking slabs of seafloor. The long-lost Farallon plate was prominent in the images as an arching slab 1,000 miles below the eastern coast of the U. S.