The influence of a stratified rheology on the flexural response of the lithosphere to (un)loading by extensional faulting

We present a two-layered finite different model for the flexural response of the lithosphere to extensional faulting. the model allows for three modes of flexure: 1) fully coupled, with the upper crust and mantle welded together by the lower crust; 2) fully decoupled, with the upper crust and mantle behaving as independent layers; and 3) partly decoupled, signifying that the response of the upper crust to small-wavelength loads is superimposed on the response of the entire lithosphere to long-wavelength loads. Which of these modes of flexure is to be expected depends on the rheology and especially the thermal state of the lithosphere. Coupled behaviour is related to a cold and strong lithosphere. The Baikal Rift Zone provides a typical example for this mode of flexure. A fully decoupled lithosphere is an exceptional case related to anomalous high temperatures in the lower crust, and is oberved in the Basin and Range province. The most common case is partly decoupled lithosphere, with the degree of decoupling depending on the thickness and viscosity of the lower crust. This is inferred, for example, for the Bay of Biscay margin.