Two end-member classes of models (indentation and mantle subduction) that have been proposed to explain patterns of crustal deformation during continental collision may be reconciled using a model that includes a combination of indentation from the side and basal forcing from underlying subducting layers. Measurement of the width of deformation across strike can be used to indicate the predominant forcing mechanism and shows that the combined case is controlled by mantle subduction if the crust is well coupled to the underlying mantle lithosphere, or by indentation if the crust and mantle lithosphere are decoupled. An increase in the width of deformation with convergence as a result of the effect of gravity on crustal thickening can cause a change in the primary control of an orogenic system from mantle subduction to indentation; this transfer may be enhanced by diffusional or convective heating at the base of the thickened crust. The India-Eurasia collision is an example where the deformation width may initially have depended on mantle subduction, but is now controlled by the indenter limit.

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