MANTLE PLUMES: The Lithospheric Thinning Process

Hi guys! Today I hope to share some basic information about mantle plumes on the Earth. In my earlier post, I have mentioned that the processes of mantle plumes caused the separations of landmass from each other. Regarding that post, I thought to talk about the mantle plumes according to my knowledge.

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Mantle plumes are the tectonically active geographical areas on the Earth surface. These plumes are originated deep inside of the Earth and form the places on Earth where low-density mantle materials upwelling continuously onto the Earth's surface. According to the depths that plumes occur originally in the Earth's interior, there are three types of plumes around the world. They are,

1. Primary or deep boundary plume – occurs around the depths of about 2900km at the core-mantle boundary.
2. Secondary plume – occurs as a synchronized plume of a large deep plume dome.
3. Tertiary plume – occurs in shallower depths around 670km at the base of the upper mantle.

The inner activities and the processes of mantle upwelling are believed that leads the plate tectonic settings around the Earth.

When going down into the Earth, the mantle materials are subjected to high temperature and pressure gradients. These gradients start the convectional flows within the mantle materials. Due to the temperature differences from top to bottom, the mantle materials are always heated and become less dense and these fewer density materials are continuously coming up towards the lithospheric base. When these mantle materials are subjected to pressure gradient and make heavy and strong hits beneath the lithosphere. These material movements lead to the formation of convectional flows beneath the lithosphere. When two divergent flows meet each other, they follow the extensional stress fields and trigger the thinning of the lithospheric crust.

Over several million years, these processes start the lithospheric rifting and series of flood basalts over the surface. Heating of the lithospheric base makes the partially melted mafic magma and they make massive volcanic eruptions. These massive eruptions lead to further rift formations and split the supercontinents apart. These massive flood basalts are providing evidence for the formation of continents that we see now.

The first starting forces for the continental rifting is still doubtful and arguing to make a certain theory. In that case, some are saying that the lithospheric thinning due to mantle plume activities are triggering the formation of the rift on the surface while others saying that the tectonic forces and stress fields cause to make rifts on the surface rather than lithosphere thinning by plume activities. However, most scientists are believing that those tectonic forces and plume activities equally contribute to the formation of rifts on the surface.

So I hope you may get a basic idea about the mantle plume processes beneath the surface from this post and I hope to see you with another post again.