| transition zone [tran`zish·ǝn ´zōn] FLUID MECHANICS Those conditions of fluid flow in which the nature of the flow is changing from laminar to turbulent. GEOLOGY 1. A region within the upper mantle bordering the lower mantle, at a depth of 246-600 miles (410-1000 kilometers), characterized by a rapid increase in density of about 20% and an increase in seismic wave velocities. 2. A region within the outer core, transitional to the inner core. |