Deformation zones in models and nature

Field studies encounter several complicating factors not studied in the models. Examples are oblique convergence, heterogeneous materials and thermal softening by intruding magmas. Within the deeply eroded Svecokarelian orogeny, studies in eastern Bergslagen indicate strain accommodation of the N-S orogenic shortening by regional E-W folding and shear along the conjugate Singö Shear Zone and Ornö Banded Series. Rising temperature resulted in migmatites affecting the strain accommodation resulting in decoupling and rotation of folds along one of the deformation zones. Deformation zones developed in convergent orogens have been studied in both analogue models and in nature. These studies have focused on a number of important factors controlling strain accommodation during orogenesis. The models show that the shape of the leading edge of the indenting continent controls whether the initial suture remains active or if an effective indenter develops, the spacing and number of faults, the width of the orogen and the height of the mountains. All these characteristics depend on the rate and spatial distribution of erosion and sedimentation. Erosion decreases the importance of effective indenters and favors shearing on existing faults leading to steeper, longer lived shears bounding narrow orogens. If sediments load the margin (e.g. foreland), the thrusts propagate further outboard widening the orogen. The strain that is accommodated by compaction and shearing along deep décollement and conjugate imbricate shears is episodic in time. This work links episodes of increased rates of erosion and sedimentation to episodes of high uplift rates, i.e. the development of new imbricate thrusts or pop-up wedges