Rheological stratification of the lithosphere

Abstract The rheology of the lithosphere is estimated on the basis of pore-pressure dependent frictional failure in the brittle regime, and power-law steady-state creep in the ductile regime. Different petrological models of the continental and oceanic lithosphere, combined with different geotherms and thicknesses, are used to generate models covering a variety of geodynamic situations. Results show that the depth-dependence of lithospheric rheology varies with the tectonic province, and that in many instances the continental lithosphere has one (at the bottom of the crust) or two (the previous one plus another at mid-crustal levels) soft ductile layers sandwiched between brittle layers. The depth distribution of geophysical parameters (seismicity, seismic wave velocity, and electrical conductivity) matches the theological predictions well. The lithospheric rheological profiles are used to analyze observed variations in the structural style of deformed continental margin and oceanic terranes in the southeastern Canadian Cordillera. The large-scale characteristics of the system show a satisfactory agreement with the inferred rheological structure. Sub-horizontal decollements should be the rule rather than the exception where the lithospheric rheology is strongly stratified.