Lateral strength variation in the lithosphere: a key parameter for the localization of intra-plate deformation

Lateral variation of strength in the lithosphere is an important factor controlling the localization of intra-plate deformation. Pre-existing heterogeneities in the lithosphere can become reactivated both in extension and compression, governing the spatial and temporal development of intra-plate deformation.
Analogue models investigating the deformation pattern and topography development of compressional intra-plate settings are presented. The initial geometric and rheological conditions are representative for continental sedimentary basin reactivation under compression. Lateral heterogeneity is introduced by the presence of a strong block located in the center of the model and striking perpendicular to the compression direction. The increase in strength with respect to the reference lithosphere, characterized by a uniform four-layer brittle-ductile rheological structure, is achieved by increasing the brittle/ductile ratio in the crust. All models have been deformed in normal gravity field.
Other investigated parameters have been the strain rate, the thickness of the brittle mantle and the rheology of the ductile mantle.
Experimental outcomes show that deformation localizes along the boundaries of the mechanically stronger basin. Under-thrusting along the margin of the basin facing the compression direction is accompanied by minor back thrusts during the latest stages of deformation. A new sedimentary basin is formed, characterized by a pop-down structure and bounded by a main topographic high. This basin is progressively locked at the boundary of the old pre-existing basin.
Strain rate governs the geometry of the deep lithospheric structure. An increase in compressional velocity results in a progressively increase in asymmetry of the lithospheric root underlying the pop-down.
Brittle/ductile ratio in the lithospheric mantle determines the absence (low B/D) or presence (high B/D) of faults in the upper brittle mantle.
The presented modelling results provide valuable insight for the strain localization in intra-plate settings under various rheological configurations and are applicable to natural areas.