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Context

• A study by National Centre for Polar and Ocean Research (NCPOR) revealed that some basaltic samples in Ninety East Ridge were highly alkaline and had very similar compositions to those released by the Kerguelen hotspot in the Southern Indian Ocean.

 

Ninety East Ridge

• The Ninety East Ridge is an aseismic ridge located almost parallel to 90 degrees east longitude in the Indian Ocean. It is approximately 5,000 kilometres in length and has an average width of 200 km.

Aseismic ridge Aseismic ridge is a long, linear and mountainous structure that crosses the basin floor of some oceans. Earthquakes do not occur within aseismic ridges, and it is this feature that distinguishes them from oceanic spreading centres. Aseismic ridges are formed by a hotspot in the mantel under the Earth's crust. As a tectonic plate moves over the hotspot, a series of seamounts can form on the ocean floor over a period of millions of years. This may be in the form of mountains, guyots or undersea plateaus.

 

Kerguelen hotspot

• The Kerguelen hotspot is a volcanic hotspot at the Kerguelen Plateau in the Southern Indian Ocean.
• The Kerguelen hotspot has produced basaltic lava for about 130 million years and has also produced the Kerguelen Islands, Naturaliste Plateau, Heard Island, the McDonald Islands, the Ninety East Ridge and Rajmahal Traps.

Volcanic Hotspots In geology, hotspots are volcanic locales fed by underlying mantle that is anomalously hot compared with the surrounding mantle. Examples include the Hawaii, Iceland, and Yellowstone hotspots.

 

Findings of the new Study

• Some basaltic samples in Ninety East Ridge were highly alkaline and had very similar compositions to those released by the Kerguelen hotspot in the Southern Indian Ocean.
• The minimum age of the alkaline samples was about 58 million years, much younger than the adjacent oceanic crust surrounding Ninety-east ridge (around 82-78 million years old). This observation was highly unusual.

 

Plausible reason

• The new study proposes that the Indian tectonic plate, which was contemporaneously moving northward at a very high speed, had dragged a considerable amount of Kerguelen plume material for more than 2,000 km underneath the Indian lithosphere.
• Subsequent reactivation of deep fractures may have triggered melting of the underlying plume material. They were then emplaced as magmatic sills and lava flows near the Nighty East Region around 58 million years ago.

 

 

MANTLE PLUME A mantle plume is an area under the rocky outer layer of Earth, called the crust, where magma is hotter than surrounding magma. Heat from this extra hot magma causes melting and thinning of the rocky crust, which leads to widespread volcanic activity on Earth's surface above the plume. Hot spot volcanoes occur far from plate boundaries. Because the hot spot is caused by mantle plumes that exist below the tectonic plates, as the plates move, the hot spot does not, and may create a chain of volcanoes on the Earth's surface.

 

The Indian continental plate was a part of Gondwanaland. It broke away from Antarctica, Australia and Africa during the supercontinental break-up. Since then, the Indian lithosphere has experienced several mantle plume eruptions underneath it.

1. Geological evidence of the Panjal trap at ~280 Ma is the oldest large igneous province within the Indian plate.
2. At ~120-117 Ma, one small pulse of the Kerguelen plume probably created the Rajmahal trap.
3. Later, Kerguelen erupted in large volume and formed the gigantic Kerguelen plateau at ~100 -95 Ma. But most of this eruption took place within the oceanic lithosphere leaving the Indian continental lithosphere unaffected.
4. Marion plume erupted ~90 Ma, which was very close to the southern Indian craton and could have started affecting the dynamics of the Indian plate.
5. Finally, the Réunion plume erupted ~65Ma directly underneath the Southern Indian craton, significantly influencing the plate motion, lithosphere thickness, and India- Eurasia collision.

NCPOR The National Centre for Polar and Ocean Research, (NCPOR) formerly known as the National Centre for Antarctic and Ocean Research (NCAOR) is an Indian research and development institution, situated in Vasco da Gama, Goa. It is an autonomous Institution of the Department of Ocean Development (DOD), Ministry of Earth Sciences, which is responsible for administering the Indian Antarctic Programme and maintains the Indian government's Antarctic research stations, Bharati and Maitri. NCPOR was established as NCAOR in 1998.

 

https://www.downtoearth.org.in/news/environment/study-gains-new-insights-into-a-fundamental-question-in-geology-83666