The concept of a lithosphere

Abstract

The current tendency to define a lithosphere as an clastically distinct region is in danger of distorting an important qualitative insight into the tec tonic processes of a planet. Just as we recognise on a laboratory scale that a given material can behave quasi elastically (solid-like) or quasi viscously (liquid-like) under different regimes or loading, it is suggested that the word lithosphere be used to describe that part or a planet. if any, that behaves quasi elastically under the stresses associated with the heat transfer process. The delimiting of such a region necessarily involves a discussion of the non elastic behaviour of planetary material. This idea is developed in particular for the Earth, although reference is made to other planets. Such a lithosphere is much thinner than one based on the depth of 'the low velocity layer' and is probably several times thicker under continents than ocean s. This is very relevant to the stability, and hence radiogcnic age of the lithosphere in the two regions. A quite distinct explanation or the oceanic low velocity layer is offered.