Tectonic plate dragging plume material: Study gains new insights into a fundamental question in geology

Source: The post is based on the article “Study gains new insights into a fundamental question in geology” published in Down To Earth on 13th July 2022.

What is the News?

A study by a team of scientists at the Goa-based National Centre for Polar and Ocean Research (NCPOR) has brought new insights into the critical processes involved in the movement of the earth’s tectonic plates.

Background

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. This study has thrown some light on it.

About the study

Scientists studied samples of igneous rocks collected from near the Ninety East Ridge in the Indian Ocean during an expedition under the International Ocean Discovery Program(IODP).

Note: IODP is an international marine research collaboration that explores Earth’s history and dynamics using ocean-going research platforms to recover data recorded in seafloor sediments and rocks and to monitor subseafloor environments.

– 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 km in length and has an average width of 200 km.

Key Findings of the study

The study has revealed that some basaltic samples were highly alkaline and had a very similar composition to those released by the Kerguelen hotspot (volcanic hotspot at the Kerguelen Plateau in the Southern Indian Ocean).

In addition, the minimum age of 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 study proposes that the Indian Tectonic Plate which was 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.