lithosfärasthenosfärgränsen

The lithosfärasthenosfärgränsen, often referred to as the lithosphere-asthenosphere boundary or LAB, marks the transition between the rigid, uppermost layer of the Earth's mantle, the lithospheric mantle, and the more ductile, underlying asthenosphere. This boundary is not a sharp, planar interface but rather a zone of gradual change in material properties, particularly mechanical strength and temperature. Geologists interpret the LAB as the depth at which the mantle rocks become sufficiently weak and ductile to flow over geological timescales, allowing the rigid lithospheric plates to move.

Understanding the LAB is crucial for plate tectonics theory. The lithosphere, composed of the crust and the uppermost rigid mantle, is broken into tectonic plates that "float" and move upon the asthenosphere. The viscosity contrast between these two layers dictates how these plates behave. The exact depth of the LAB varies significantly across the Earth's surface, being deeper beneath old, thick continental lithosphere and shallower beneath young, oceanic lithosphere. Factors influencing its depth include temperature, composition, and the presence of melt within the asthenosphere. Seismic imaging, particularly the analysis of seismic wave velocities, is a primary tool used by scientists to infer the location and characteristics of the LAB. Changes in seismic wave speeds indicate variations in rock properties, helping to delineate this critical boundary.