Upper Mantle: an intermediate discontinuity known as the Repetti discontinuity allows the distinction between the Upper Mantle (Asthenosphere) and the Lower Mantle. Its upper boundary, which is the contact with the overlying Earth’s Crust, lies between 30 and 50 km below the surface and is called the Mohorovicic discontinuity (Moho). It extends down to about 400 km in depth and is composed of ultramafic rocks with a composition very similar to Peridotites. The Upper Mantle can be further divided into several layers:
- Lithospheric Mantle: the mantle immediately beneath the Moho, extending to about 110–113 km below the continents.
- Asthenosphere: the layer beneath the lithosphere, extending down to approximately 400 km.
- Transition Zone: the zone below the asthenosphere, extending to depths of about 650–700 km.
- Mesosphere: the layer that includes both the Intermediate and Lower Mantle, reaching depths of approximately 2,900 km.
