What is the secret behind the giant gravity hole in the Indian Ocean called the geoid depression? | Science

Researchers have determined the origin of the giant geoid depression by modeling how tectonic plates slid over Earth’s hot, sticky mantle over the past 140 million years.

Beneath the Indian Ocean lies a giant gravity well, estimated to be about 3 million square kilometers in size, where the ocean floor sinks into a vast depression, where the gravitational forces are greatly weakened.

Oceanographic surveys and satellite measurements have revealed that sea level falls near the tip of the Indian subcontinent due to the difference in gravity between points of gravity and surrounding gravity wells, called geologic lows under the Indian Ocean. .”

Plate grave

And I tried Many studies The explanation for tectonic subsidence under the Indian Ocean is that it is caused by remnants of a previous plate sinking into the Earth’s crust under another plate millions of years ago. However, there is no definitive explanation.

Other researchers have used seismic waves to image the Earth’s interior in three dimensions to study mantle convection as material sinks down.

They found that the lighter material in the upper and middle mantle below the geoid accounts for the low gravity in this region. Most current theories have tried to explain this anomaly in the lower geoid with the help of dense, cold oceanic plates that sank into the mantle in the past.

In 2018, a team of scientists from India’s National Center for Polar and Ocean Research – on board a ship – set out to map the geoid trough and distribute a series of seismic measurements on the sea floor in the target area.

The team was able to track hot flows of molten rock rising beneath the Indian Ocean. Of course, it is necessary to look for a scenario that explains the formation of a geoid depression in its early stages.

Origins and Determinants

According to A statement Published on the “Science Alert” website (Science Alert) researchers have determined the origin of the giant geoid depression by modeling how tectonic plates slid over Earth’s hot and viscous mantle over the past 140 million years.

During that period, the Indian tectonic plate broke away from the supercontinent Gondwana and began its march northward. As the Indian plate separated, the ancient Tethys sea floor sank into the mantle and the Indian Ocean opened up.

And inside study Published last May in the journal Geophysical Research Letters, geologists Dipanjan Pal and Adri Ghosh of the Indian Institute of Science’s Center for Geology in Bangalore said, “Previous studies have all studied gravitational deformation within the geoid depression, but they haven’t been concerned with how he grew up.”

Researchers believe the answer lies more than a thousand kilometers beneath the Earth’s crust, where the cold and dense remnants of an ancient ocean sank into a “plate grave” beneath Africa about 30 million years ago, moving hotly. Rock magma. The researchers believe that the lighter material at the top of the middle part of the mantle is responsible for the weakening of gravity in this region.

Hot magma flow

To reach these conclusions, Paul and Ghosh used more than 10 computer models to simulate the motion of the plates and the motion of the mantle, and compared the pattern of oceanic subsidence predicted by those models to observations documented from geoid depressions. .

The two researchers worked with ten samples — which they hypothesized were flows of low-density hot magma rising from beneath the geoid depression. This geoid depression, in addition to the structuring role of the mantle layer, is formed by buoyant flows to a sufficient height.

“Our results suggest that the outflow must be buoyant enough to ascend to mid-depth to match the existing geoid depression in terms of shape and height,” the researchers wrote.

The paper said the first flows from these thermal layers originated about 20 million years ago south of the geologic low in the Indian Ocean, and about 10 million years after the ancient Tethys Sea sank into the lower mantle. The tectonic subsidence increased as the flows spread beneath the crust and approached peninsular India.

Because the findings are consistent with elements of Gauche’s previous modeling work in 2017, the geologist duo suggested that the flows appeared after the ancient Mediterranean-Tethys sea floor sank into the lower mantle, disrupting the famed “Africa block.”