A scientist from the University of Wyoming, using a computer model, tested the hypothesis that sand and mud weathered off the coast of California about 75 million years ago sank deep into the earth's crust, and then rose and turned into mountains.
According to the scientist, sand and mud, which for a long time traveled under the earth's crust, like huge drops of paraffin in a modern lava lamp, then floated to the surface of the planet far from the California coast - in the Mojave Desert in Arizona.
"These rocks aren't the most beautiful to look at, but they've been on an extraordinary journey and have an incredible story to tell," says University of Wyoming geophysicist Jay Chapman, who specializes in tectonics.
Chapman outlined the history of the travel of stones in a scientific article, which was published by the journal Geology.
“The stones began life as sedimentary material that was weathered from the Sierra Nevada mountains, carried by rivers and streams into the ocean and then settled in a depression at the junction of tectonic plates, similar to the modern Mariana Trench,” says Chapman. “Then one of the plates, plunging, dragged the materials that had settled in it with it about 20 miles deep into the Earth. At this depth, these deposits turned into a rock called shale. This in itself is quite surprising, but the main feature of these stones is that they did not remain at a depth. but somehow returned to the surface. And you can stand on them today."
Scientists call the linear joints of lithospheric plates subduction zones and study these zones especially carefully. There the plates collide, one can sink under the other and drag the surrounding structures with it. And then mineral deposits are formed in these places. This is why scientists are so interested in these zones.
How did sedimentary rocks submerged in the earth's crust return to the Earth's surface? And how are they distributed in its bowels? These are just a few of the questions that Chapman is trying to answer in his research.
“The prevailing theory is that sedimentary material was smeared across the base of the North American tectonic plate and pressed against it. Eventually, they formed a layer like a thin sheet,” says Chapman. “However, the density of these deposits is much lower than the density of rocks in the mantle or lower Computer simulations show that over the millions of years that pass after submersion under the slab, these materials, due to their fluidity, should gradually rise smoothly, like hot wax in a lava lamp."
The study is important for understanding the processes occurring in subduction zones, and for understanding the logic of the distribution of natural resources.
"Geophysicists around the world are trying to understand what determines the unique composition of the continental crust, and the subduction and reintroduction of [former] sedimentary rocks is a popular hypothesis," Chapman says. submerged sediments, determine the concentration of economically important minerals and metals."