What two zones is the mantle divided into?

1 Answer
Sep 15, 2016


The Earth's mantle consists of an upper mantle and a lower mantle.


The difference between these two layers of the mantle comes from the predominant mineral phases in the rock. Both the upper and lower mantle consist primarily of silicate minerals. But under high pressure in the lower mantle the familiar silicate structure, where four oxygen atoms are bonded tetrahedrally to each silicon atom, gives way to a more ionic structure where each silicon is bonded to six oxtgens (https://en.wikipedia.org/wiki/Silicate_perovskite).

The mantle is often further subdivided. A more complete description of its structure includes the following:

Lithosphere: The uppermost part of the uppr mantle, continuing into the crust, is the rigid outer structure of Earth's rock.

Asthenosphere: Most of the upper mantle is hot enough, above 1300°C, for its rock to undergo plastic flow.

Transition zone: The boundary between the upper mantle and the lower mantle is not sharp, but contains a complex transition between the two predominant silicate phase structures.

Lower mantle: As noted above, with its octahedrally bonded perovskite silicates.

Core-mantle boundary: Another transition zone, this one between the rocky lower mantle and the metallic, iron-rich upper core.

More details are given at https://en.wikipedia.org/wiki/Mantle_(geology).