Missing Continental Crust Sank, Study Shows

By Rodney Rafols , Oct 06, 2016 03:29 AM EDT

Millions of years ago a massive collision between the Eurasian plate and the Indian plate has created one of the most impressive mountain ranges, the Himalayas. For many years geologists have wondered what happened to the crust between the two plates after the collision. Now there might be some answers about it.

Three geoscientists from the University of Chicago are studying what happened after the Eurasian and Indian plates collided. One result could be seen in the Himalayas, but there is far more material that has disappeared after the event. This material is the continental crust.

"What we found is that half of the mass that was there 60 million years ago is missing from the Earth's surface today," Miquela Ingalls, graduate student in Geophysical Sciences from the University of Chicago and lead author of the project, said. She is doing the project as part of her doctoral work, as the UChicago News reports.

For a long time plate tectonics theory holds that the continental crust is buoyant and can't go below the mantle. That has been one of the tenets of place tectonics. Oceanic crust might be able to slide under the mantle, but continental crust doesn't. At least that's what's been taught before Ingalls and her team have found out.

"We really have significant amounts of crust that have disappeared from the crustal reservoir, and the only place it can go is into the mantle," David Rowley, Professor in Geophysical Sciences and one of the advisors for the project, said. This conclusion came about after the researchers used data on how large the two plates were before the collision. They have used 20 years of data that estimates how the thick the Earth's crust was then.

Some of the material from the collision can be accounted for, as the Himalayas are there as a testament to that event. Some were also said to have been thrust to the side and formed what is now Southeast Asia, as Phys Org notes. Ingalls though said that even after accounting for them, half of the continental crust at the time of the collision could not be accounted for. The only explanation would have to be that material has been thrust back into the Earth's mantle.

With this theory, it can now we explained why some elements such as lead and uranium can be found during volcanic activities. Such elements can be found mostly from continental crust, but not much from the mantle. Plate tectonics explain much about the Earth, such as the discovery of a recent fault line in Southern California.

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