Mantle Plumes and Tectonic Plates

Mantle Plumes and Tectonic Plates

Subject: Geography

Mantle Plumes and Tectonic Plates

• Indian tectonic plates dragged a considerable amount of Kerguelen plume material for more than 2,000 km underneath the Indian lithosphere, a study finds.
• The buoyant rising of hot and low-density magma or plumes from the Earth’s interior towards the surface leads to extensive volcanism and the creation of seamounts and volcanic chains above the ocean floor.
• However, a rising plume has to cut through the thick overlying lithosphere, the most rigid part of the earth, before it can reach the earth’s surface.
• Many times, the magma’s buoyant force is not sufficient to pierce through the lithosphere.
• In such cases, plumes tend to dump the material at sub-lithospheric depths. When the tectonic plates that lie over the lithosphere move, they tend to drag the ponded materials along with them.
• A fundamental question that remains outstanding in understanding earth’s processes is how far a tectonic plate can drag the plume material at its base after its initial impact with the plume.
• The recent study at NCPOR (National Centre for Polar and Ocean Research) has thrown some light on it.
• The team of scientists studied samples of igneous rocks collected from near the Ninety East Ridge in the Indian Ocean.
• 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 kilometers in length and has an average width of 200 km.

Findings

• A detailed geochemical and isotopic investigation revealed that some basaltic samples were highly alkaline and had very similar compositions to those released by the Kerguelen hotspot in the Southern Indian Ocean.
• In addition, 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).
• 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 decompression melting of the underlying plume material and emplaced as magmatic sills and lava flows near the Nighty East Region around 58 million years ago.