Sands from Grand Canyon rocks came across the continent
Material from the Appalachian mountain range on the east coast of North America played a key role in shaping the mighty sandstone deposits of the Grand Canyon in the western United States, report Bill Dickinson of the University of Arizona in Tucson and his colleagues. The researchers suspect that giant rivers carried the grains west, where they were deposited along an ancient shoreline in Wyoming and eventually blown south into dune fields by the winds. About half of the rock material, the scientists estimate, could have made this journey of thousands of kilometers and solidified into sandstone 300 to 150 million years ago.
On the other hand, only a quarter of the sand apparently comes from the forerunners of today's Rocky Mountains, which were previously assumed to be the main source of the rock material. Another quarter came from the interior of Canada.
The researchers had analyzed zircons in the rocks. These minerals contain radioactive uranium, which, after solidifying from the molten magma, decays into lead. By analyzing the degree of decay, the scientists were able to date the original age of the zircons and compare them with rock samples from other regions. About half of the samples showed formation dates of about 1.2 billion or 500 million years, matching the age of the granites in the Appalachian Mountains.