Читать книгу Engineering Physics of High-Temperature Materials - Nirmal K. Sinha - Страница 19

CRUST

MANTLE

CORE

Earth is believed to be a sphere with three concentric zones: the crust, the mantle, and the core. The solid shell of the earth, including the crust and the uppermost relatively rigid layer of the mantle, is known as the lithosphere, whereas the weaker zone beneath this layer is known as the asthenosphere. The division between the two layers is rather qualitative, based on seismic response, and improved understandings can be made on the basis of rheological response of geologic materials as a function of temperature.

The mantle is subdivided into an upper boundary marked by the Mohorovicic discontinuity, a lower boundary marked by Gutenberg discontinuity, and the core (also further subdivided into the inner core and the outer core). Discussions on these subjects are outside the scope of this book. However, we will consider the lithosphere and asthenosphere as one “solid” layer at various temperatures below the melting point of all rocks. The topic is rather complex because of the inhomogeneity in the structure and the melting point depends on pressure and mineral contents.