Lithosphere-asthenosphere boundary

Boyd F. R. (1987) High- and low-temperature garnet peridotite xenoliths and their possible relation to the lithosphere-asthenosphere boundary beneath southern Africa. In Mantle Xenoliths (ed. P. H. Nixon). Wiley, London, pp. 403 -412. 

Numerical and analytical models of the vertical and lateral flow of hot, buoyant plume material beneath variable thickness continental lithosphere show that steep gradients at the lithosphere-asthenosphere boundary (LAB) strongly influence the distribution of plume material, and, consequently, the location and volume of melt. Cratonic keels deflect the plume material, with only minor thinning and heating of the mantle lithosphere beneath the cratons. 

Figure 3.1 A cross section of the crusts, rigid upper mantle, and plastic mantle asthenosphere of the Earth. The Mohorovicic Discontinuity is the boundary between the crust and upper mantle. The lithosphere includes the crusts and the upper mantle.

FIGURE 3.10 The thermal structure of old oceanic lithosphere over asthenosphere with a (normal) potential temperature of 1,280°C (the term potential temperature is defined in Section 3.1.4.3). The curve shows the horizontally averaged equilibrium thermal structure of oceanic lithosphere and asthenosphere (after White, 1988). Also shown are the rigid MBL, the thermal boundary layer, and the adiabatic interior of the upper mantle. The lithosphere is sometimes referred to as the "conductive lid" of the mantle, as opposed to the convecting interior (asthenosphere). 

The pressure given by the N positions are estimated from the accepted correspondence of 0. 1 GPa pressure to 3 km depth into the earth crust. The lower pressure limit of N is given by the boundary zone between the upper region lithosphere and the mobile asthenosphere at about 150 km in the earth s mantle. 

Convergent boundaries where plates move toward each other. One plate may be pushed beneath the other in a subduction zone in which matter is buried in the asthenosphere and eventually remelted to form new magma. When this does not occur, the lithosphere is pushed up to form mountain ranges along a collision boundary. 

---