Mathematical models have been constructed of the geometric, thermal and flexural-isostatic response of the lithosphere to extension by faulting (simple-shear) in the upper crust and plastic, distributed deformation (pure-shear) in the lower crust and mantle. Models involving upper-crustal extension by both listric and planar faults have been developed. These coupled simple-shear/pure-shear models have been used to calculate extensional sedimentary basin geometry, subsidence history and crustal structure. Basin geometry and subsidence history are controlled by fault geometry (planar or listric), the amount of fault extension, fault dip, the depth of the transition from simple-shear to pure-shear, and the flexural rigidity of the lithosphere during both syn-rift and post-rift stages of basin formation. For the planar fault model, footwall and hangingwall blocks are considered to behave as two interacting flexural cantilevers; the response of these cantilevers to the isostatic forces produced by extension generating footwall uplift and hangingwall collapse. For a set of adjacent planar faults the lateral superposition of flexural footwall uplift and hangingwall collapse generates the familiar ‘domino’-style block-rotation of such multiple fault systems. The listric fault model assumes that the hangingwall collapses onto a rigid footwall by vertical shear, and that the tectonic denudation of the upper crust by faulting generates isostatic uplift producing limited footwall uplift. Deep seismic reflection data and earth-quake seismology suggest that the fundamental basement faults controlling lithosphere extension are planar. It is argued that the vertical shear construction of hangingwall collapse onto a rigid footwall is inappropriate for basement response. The coupled simple-shear/pure-shear models of extensional basin formation, using both listric and planar fault geometries, have been applied to the formation of the Jeanne d’Arc basin, Grand Banks, and the Viking Graben of the northern North Sea. The numerical modelling shows that the crustal thinning, thermal and sediment-fill loads generated during and after lithosphere extension need to be distributed flexurally in order to generate the observed basin depth and geometry. The flexural-cantilever, planar-fault model provides closer agreement to observed basin depth and subsidence than the listric-fault model. The planar fault model also produces more footwall uplift than a listric fault model. Erosion of this footwall uplift generates substantial isostatic uplift through unloading, leading to a large underestimate of the horizontal displacement on basin-bounding faults. The low values of effective elastic thickness obtained by extensional basin modelling are substantially less than the thickness of the cool, brittle upper crust. It is suggested that flexural bending stresses associated with lithosphere extension on planar faults are sufficiently large to generate brittle failure within the upper crust, so producing the low values of effective elastic thickness. This is consistent with the predictions of the flexural-cantilever model.

A combination of fieldwork, basin analysis and modelling techniques has been used to try and understand the role, as well as the timing, of the subsidence -uplift mechanisms that have affected the Azerbaijan region of the South Caspian Basin (SCB) from Mesozoic to Recent.Key outcrops have been studied in the eastern Greater Caucasus, and the region has been divided into several major tectonic zones that are diagnostic of different former sedimentary realms representing a complete traverse from a passive margin setting to slope and distal basin environments. Subsequent deformation has caused folds and thrusts that generally trend from NW-SE to WNW-ESE.Offshore data has been analysed to provide insights into the regional structural and stratigraphic evolution of the SCB to the east of Azerbaijan. Several structural trends and subsidence patterns have been identified within the study area. In addition, burial history modelling suggests that there are at least three main components of subsidence, including a relatively short-lived basin-wide event at 6 Ma that is characterized by a rapid increase in the rate of subsidence.Numerical modelling that includes structural, thermal, isostatic and surface processes has been applied to the SCB. Models that reconcile the observed amount of fault-controlled deformation with the magnitude of overall thinning of the crust generate a comparable amount of subsidence to that observed in the basin. In addition, model results support the tectonic scenario that SCB crust has a density that is compatible with an oceanic composition and is being under-thrust beneath the central Caspian region.

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