Geologists have used a model that geologist Émile Argand came up with in 1924 to understand the Himalayas. The model said that the mountains were held up by a double-thick crust. The Indian tectonic plate sank far under the Asian plate, building layers of crust to a depth of 70–80 km (about 45–50 miles), according to this theory. But a new study is now questioning that long-held idea.
A new research in the journal Tectonics says that sophisticated computer models show a more complicated structure: a hard slab of mantle rock is jammed between the Indian and Asian crusts beneath the Himalayas. This “crust-mantle-crust sandwich” makes the mountain range’s base stronger and more buoyant. This fits better with what we already know about seismic and geological data.
The Argand model, which has been around for a hundred years, thought that merely layers of crust held up the mountains. Simone Pilia, one of the study’s authors, says that rock at depths of about 40 km becomes ductile, or “like yogurt,” which means it is too weak to hold up the huge weight of the range in a straightforward stack. Geoscientists have long recognized several strange things about the earth’s crust that didn’t match with the traditional “crust-stack” model. The new “mantle-sandwich” model overcomes these long-standing problems. Pilia says that things that “seemed to be mysterious” now make perfect sense.
This new information has a big effect on how we think about tectonic activity and seismic danger in the Himalayas, which is one of the most seismically active places on Earth. The thick Tibetan crust is floating on a much stronger basis since there is a buried mantle slab underneath it. This could change how stress builds up along the fault line where the Indian and Asian plates meet. The collision still pushes the Himalayas up by roughly 1 centimeter each year, but it also causes earthquakes that can be very dangerous. To make better models of tectonic forces and get ready for earthquakes in the area, it’s important to know how the crust and mantle really work.