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Context: National Geophysical Research Institute (NGRI) scientists from Hyderabad reveal a historic collision between India and East Antarctica over a billion years ago.
Details
Key Recent Findings
- A hidden ridge in Andhra Pradesh's Darsi and Addanki regions, suggest significant geological shifts.
- This ridge is attributed to the historic collision, suggesting a tilting of the Cuddapah basin towards the south.
- Identified both upper and lower Proterozoic Cuddapah sediments directly overlying the crystalline basement.
- The subsurface crustal seismic structure of the north Cuddapah basin a thin layer of alluvium underlain by Gondwana sediments and Proterozoic sedimentary layers.
- Seismic data reprocessing uncovered Proterozoic sediment layers, shedding new light on India's eastern coast evolution.
- The study indicates signs of past seismic activity in the area, hinting at the presence of a marginal ocean basin along the east coast during the Columbia and Rodinia supercontinent assembly periods.
Earlier Findings in 2016
- In 2016 scientists found Indian subcontinent was part of Antarctica a billion years ago but were separated and re-united several times due to tectonic movement of plates.
- The clue was from the study of continental crust in the Eastern Ghats area.
- The reason behind the separation of India from Antarctica was an ocean this ocean closed again with the movement of landmasses of the two-continent approaching each other and finally colliding again one billion years ago.
- This collision formed the Eastern Ghat mountain belt.
2021 study claim
- Study tested the two-part separation model by conducting magnetic and seismic surveys in an effort to make estimates about the age of the rock and thickness of the crust more accurate.
| Magnetic anomalies are magnetic variations within rocks that help in understanding the formation of the seafloor. Seismic data helps to know the composition of the rocks. |
- The researchers found that the Indian block started to separate in the eastern part of Antarctica at 132 Ma and drifted northwards more or less continuously.
- The southern tip of the Indian plate, Sri Lanka, was detached from Antarctica at some 112 Ma, much later than the two-phase model predicts.
- It claims the Elan Bank and SKP didn’t break off from the drifting Indian plate, but were formed by volcanism from a large area of hot material in the Earth’s mantle.
- Magma from this volcanism alsomigrated under the floating Indian block to create eruptions of the Rajmahal hills.
Elan Bank and the Southern Kerguelen Plateau (SKP)
According to the two-part separation theory, about 120 million years ago, a bit of land and some continental fragments broke off from the Indian plate.
These came to be known as the Elan Bank and the Southern Kerguelen Plateau (SKP), which lie embedded on the ocean floor of the Antarctic plate.
The new theory claims the Elan Bank and SKP did not separate from the Indian plate at all, but instead were formed by volcanism after the plate separated.
Original theory
- The Indian subcontinent is believed to have been a part of an ancient supercontinent called Gondwana, which also comprisedmodern-day Antarctica, Africa, South America, Australia, Arabia and Madagascar, and took shape 600 million years ago.
- The first breakup of this supercontinent is estimated to have begun 180 million years ago.
- Around 132 Ma (mega annum, million years) ago, when Greater India broke away from Antarctica and Australia, there was a small lake between them.
- As it started to drift northwards, this lake began to expand to form the Indian Ocean.
- At the same time, under the ocean, a large volcanic feature called the Kerguelen Plateau very close to Antarctica.
| An underwater plateau is a flat elevated stretch of crust that is higher than the surrounding land. |
- About 130 million years ago, when the Greater India block was still closer to Antarctica than Eurasia, Sri Lanka started to separate from India while the Indian plate was still supporting it.
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Original theory methodology
To determine how the present-day landmasses came to be, geologists drill, scan and date rocks and seafloor beds.
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- The advocates of the two-part separation theory came up with their conclusion after drilling in the Kerguelen plateau and the Elan Bank.
- They found pieces of continental rocks, which are generally less dense and much older than oceanic rocks, surrounding and underneath the newer oceanic rocks on the seafloor.
- This indicated that they came from a continent rather than formed right there on the seafloor.
- Greater India was once attached to the Kerguelean plateau, evident from the Rajmahal hills in Jharkhand, which was the site of long-duration, slow basaltic volcanism from the volcanic region called the Rajmahal traps.
- A previousstudy, conducted in 2002, proposed that Rajmahal hills and the Southern Kerguelen Plateau formed at the same time.
- The scientists then compared this with the volcanic rock of the Kerguelen plateau and it was found be of the same age and type.
- The Kerguelen plateau was attached to the Rajmahal-Sylhet Line near the Shillong Plateau.
Limitations of new study based on seismic and magnetic experiment
- It cannot provide the age of the oceanic rocks it can only provide the nature of the rocks.
- The age of oceanic rocks can be determined by either drilling in the crust, collecting fragments and dating them in a laboratory, or by magnetic surveys.
- Magnetic surveys cannot be entirely relied upon, as this study has done, to date oceanic rocks, they shouldn’t be disturbed by newer geological processes that deposit magma on top of them, burying the original rock underneath.
- Once secondary geological processes take place and initial signatures are disturbed, it becomes difficult to correctly identify the original age of the rocks.
Other Evidence that supports the theory
- Jig-Saw-Fit:The shorelines of Africa and South America facing each other match remarkably.
- Tillite:The glacial tillite found in Gondwana system of sediments has its resemblance to six different landmasses of the Southern Hemisphere. Counterparts of this succession are found in Africa, Falkland Island, Madagascar, Antarctica and Australia besides India.
- Placer Deposits:The placer deposits of gold in the Ghana coast do not have source rock in the region. The gold deposits of Ghana have been derived from the Brazil plateau when the two continents lay side by side
- Distribution of Fossils:identical species of plants and animals adapted to living on land or in freshwater are found on either side of the marine barriers. For example remains of Mesosaurus, a freshwater crocodile-like reptile that lived during the early Permian (between 286 and 258 million years ago), are found solely in Southern Africa and Eastern South America.
NCERT
Sources:
TimesofIndia,Livemint,News18,IndianExpress.
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PRACTICE QUESTION
Q. What do you understand by Continental Drift Theory? Discuss along with the evidences that support the theory? 150 words
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