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Abstract. Geodynamical numerical modeling has been combined with crustal structural restoration of the central Pyrenees in order to gain insight into fundamental processes that control the evolution of collisional orogens. Models are based on deformation of the crust by stresses transmitted upward from kinematic basal boundary conditions corresponding to the subduction of part of the lithosphere. The influence of inherited crustal heterogeneities, denudation, subcrustal loads, and crustal mechanical properties, consistent with wellconstrained crustal partial restored cross sections of the central Pyrenees, is investigated by progressively incorporating them into model experiments. The primary result inferred from the modeling is that the asymmetry of the central Pyrenees double-wedge, seen as strain partitioning and in the morphological evolution, is a consequence of the asymmetric distribution of inherited crustal heterogeneity. The tectonic style of the central Pyrenees is the result of the inversion of the Early Cretaceous extensional fault system, during the early stages of the collision, and the reactivation of Hercynian heterogeneities during the late stages. Most of the upper crustal mass that entered the orogen during the calculated 165 km of convergence was accommodated by an increase of upper crustal cross sectional area or lost by denudation. To explain the upper crustal mass partitioning, as well as the geometry of the foreland basins and the preservation of synorogenic deposits in piggyback basins, a subduction load has to be applied to the models. Lower crust and mantle lithosphere were consumed by the mantle.

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The South Island zone of oblique continent‐continent convergence occurs along a 400 km‐long section of the modern Australia‐Pacific plate boundary zone, across which about 50 km of shortening has been accommodated since about 10 Ma. The orogen comprises a central mountain range (Southern Alps) flanked on both sides by what are interpreted to be foreland basins. Two essential features that characterize the orogen are (1) the degree of denudation that accompanied deformation, and (2) a fundamental structural asymmetry. The architectural asymmetry of the orogen can be explained by plane strain, finite element models of continental convergence incorporating mantle subduction. Comparison of model and orogen polarity implies that Pacific plate mantle subducts. The models predict two crustal‐scale dipping shear zones that form above the point where the Pacific mantle subducts. The localized one more distant from the incoming plate (retro‐step‐up shear zone) corresponds to the Alpine fault, whereas its conjugate (pro‐step‐up shear zone) corresponds to the distributed strain and thrusting along the eastern margin of the mountain belt. Parameters that modify the model boundary conditions (top surface, degree of denudation; basal zone, subduction load, crust‐mantle velocity discontinuity, subduction of lower crust, mantle retreat, and distributed decrease in mantle velocity) and the internal strength of the crust (two‐layer crust with moderate coupling, temperature distribution, strain weakening) are varied in a series of numerical model calculations that establish the combination of material properties and boundary conditions that lead to different cross sectional architectures of the modeled collision zone. In turn, these are compared with observations about the South Island orogen. The calculations show how the style and extent of deformation across the whole orogen depend on the rheological properties of the crustal layer and on the balance between its internal strength and the combined effects of the boundary and gravitational stresses. North to south along‐strike differences in the width and two‐dimensional architecture of the orogen, simulated in the experiments by varying the model parameters, can be explained by a combination of southward increases in preconvergent crustal thickness, geothermal gradient, convergence, and potentially subduction retreat, with the added possibility of a southward decrease in the component of lower crustal subduction.

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