Thermomechanical structure of European continental lithosphere; constraints from rheological profiles and EET estimates

SUMMARY The EET (equivalent elastic thickness) of the lithosphere is a measure of the integrated lithospheric strength. It is directly related to the mechanical thickness and rheology of the crustal and mantle lithosphere. We present a comparison of EET estimates and strength profiles based on the extrapolation of rock mechanics data for different parts of the European and Eurasian continental lithosphere. We discuss the temporal and spatial variations in the mechanical thickness and strength inferred from data for Precambrian segments of Europe's lithosphere, Variscan Europe and the Alpine collision belt. This analysis demonstrates important spatial and temporal variations in lithospheric rigidity for orogenic belts and sedimentary basins in eastern and western Europe and Asian parts of Eurasia. The EET estimates based on synthetic rheological profiles constrained by newly available geophysical data are consistent with the estimates of EET derived from flexural studies of sedimentary basins, forelands and orogenic belts. These rheological profiles suggest weakening of the major parts of the European and Eurasian continental lithosphere by decoupling of the crustal and upper-mantle parts- A comparison with the seismicity-depth distribution for some selected sites suggests that the intra-plate seismicity is essentially restricted to the upper crustal parts of Europe's lithosphere, providing additional support to the notion of the decoupled lithosphere. The presence of intra-plate stress fields can explain a significant part of the observed variations in EET estimates within individual thermotectonic age groups. A comparison of wavelengths of crustal and lithospheric folding with observations shows these wavelengths to be consistent with estimates of EET inferred from the rheological response of basins and orogens at more moderate levels of intra-plate stress.