In the depths of our planet’s continents rise plateaus that defy any simple explanation. No volcano, no continental collision, no cloud of rising molten rock can clearly account for their jumble of locations and dramatic features.
Using statistical analysis and simulations based on geological studies, researchers from the UK and Germany put forward a radical idea, arguing that slow instabilities triggered by cracks in the Earth’s fractured crust are behind the anomalies.
From the mountains of Brazil to the Great Depression of South Africa to the Western Ghats of India, our planet is dotted with vast, flat mountains surrounded by steep walls that dominate the landscape.
These plateaus are hundreds of kilometers from the nearest fault, on sections of the crust considered geologically stable, their birth timed tens of millions of years after the forces pushing the nearest continental rifts subsided . This makes it difficult to directly blame the Earth’s tectonic movements.
“Scientists have long suspected that, in fact, steep, mile-high topographic features called great rifts—like the classic example that surrounds South Africa—form when continents rift and eventually break apart ”, says Tom Gernon, a geologist at the University of Southampton.
Plateaus that defy any simple explanation
“However, explaining why the interior parts of continents, away from such escarpments, rise and become eroded has proven much more difficult. Does this process have anything to do with the formation of these imposing escarpments? We just didn’t know,” the scientists added.
Although it is almost certain that there is a mixture of geologic forces linking the growth of these escarpments to the breaking of the Earth, no theory accurately captures all of their characteristics.
Some hypothesize that the weathering of rocks at great depth loosens the crust from the mass, allowing it to bend into shape. Others suspect that drastic temperature differences cause convection in the mantle, pushing the rock up, or perhaps erosion and weathering are instead slicing up the coastal landscape beyond.
This new suggestion combines the processes with a slow churning of the mantle that rolls under the crust at a speed of only 15-20 kilometers every million years, he writes ScienceAlert.
Following a previous study of the processes that drag diamonds to the planet’s surface, the team found that the stretching of the crust as the plates pull apart creates instabilities in the mantle, which undulates beneath the solid lithosphere.
A mixture of geological forces
“This process can be compared to a sweeping movement that moves towards the continents and disrupts their foundations,” says Sascha Brune, a geophysicist at the University of Potsdam in Germany.
The team’s modeling suggested that the speed of the waves that would have followed the breakup of Gondwana reflected the timing of erosion around the Great Rift in southern Africa.
It is thought that this slow echo of molten rock could destroy the ancient roots of the continents, known as cratons.
Loss of material from the underlying craton and erosion of eroded surface rocks could together explain the dramatic uplift of the flattened landscape, with the team’s models accurately describing the mix of plateaus and steep escarpments across the globe.
Understanding the dynamics of processes hidden far below the surface not only helps us accurately map the changes in the landscape responsible for the formation of precious minerals and resources, but can also help us better interpret historical climate changes in relation to the rise and fall of continents.
This research was published in Nature.
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Source: www.descopera.ro
