The engines that drive the growth of the world's tallest mountains into the sky run deep beneath the planet's skin. Geologists have some idea of the mechanisms of action, but the evidence so far has left little room for debate about the details.
In addition to a new look at previous research, a recent analysis of new seismic data collected from across southern Tibet has provided a striking depiction of the giant forces at work beneath the Himalayas.
Submit in American Geophysical Union Conference In San Francisco last December, researchers from institutions in the United States and China described the disintegration of the Indian continental plate as it grinded along the bottom of the Eurasian tectonic plate that lies above it.
It is a surprising compromise on two models currently favored as explanations for the uplift of the Tibetan Plateau and the massive Himalayan mountain range.
In both cases, collision between pieces of crust belonging to India and Eurasia is responsible. Starting about 60 million years ago, the Indian plate was pushed beneath its northern neighbor as it was carried by streams of molten rock within the mantle.
Little by little, the Eurasian landmass rose skyward on the shoulders of a sinking giant, giving us the highest elevations on Earth.
Studies of mantle and crust density indicate that the fairly buoyant Indian continental plate should not sink easily, meaning that it is likely that submerged portions of the crust should still be grinding under the belly of the Eurasian plate rather than under it. She sank deep into the mantle.
Another possibility is that the Indian painting was distorted in a way that caused some parts to wrinkle and fold, and other parts to sag and sink.
Different viewpoints emerge depending on the types of evidence preferred and how the data are treated.
In an investigation conducted by Chinese Ocean University geophysicist Lin Liu, researchers combined “top and bottom” S wave And Shear wave splitting data From 94 broadband seismic stations arranged from west to east across southern Tibet, and combined with previously collected 'back and forth' P wave data To get a more nuanced view of the dynamics below.
They determined that the Indian plate was not just swaying smoothly beneath the Eurasian plate, nor was it bunched up like a rug on a slippery floor.
Instead, it disintegrates, its dense base peeling off and sinking into the mantle while its lighter upper half continues its journey just below the surface.
While computer models have suggested that thicker parts of some plates could break apart in this way, the study provides the first experimental evidence that this is happening.
The team's description is consistent with geological models based on the boundaries of helium-3-enriched spring water and patterns of fractures and earthquakes near the surface, which together support the map of the carnage below, where parts of the ancient Indian plate appear more or less intact. , and another disintegrates at a depth of about 100 kilometers, allowing the base to warp into the planet's molten core.
Having a clear 3D description of the boundaries and boundaries of plates as they rub together not only makes it easier to understand how our surface looks the way it does, but could inform future methods of earthquake prediction.
The study is due in 2023 American Geophysical Union Conference. A pre-print version of the study is Available online.
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