Models of large, hot orogens containing a collage of reworked and accreted terranesThis article is one of a series of papers published in this Special Issue on the themeLithoprobe — parameters, processes, and the evolution of a continent.

Abstract

We describe a classification scheme for orogens using Temperature–Magnitude (T–M) diagrams and use this framework for modelling large, hot orogens that evolve in continents comprising cratonic nuclei bordered by a series of juvenile accreted, reworked, and metamorphosed terranes. Modelling the complete evolution of an orogen is difficult, particularly large orogens with multiple orogenic phases. Early phases during which a continent is assembled produce a tectonic and metamorphic fabric that needs to be taken into account when modelling the main collisional orogeny. This inherited fabric is represented in a simple way in models described here by a series of lower crustal blocks that are arranged to be systematically stronger toward the cratonic continental interiors. We investigate how this fabric influences the development of the model orogen during the main collisional phase using upper-mantle-scale (UMS) and crustal-scale (CS) finite element models. The models exhibit a diachronous three-phase evolution: crustal thickening, thermal incubation, and lower crustal indentation. The UMS and CS models are shown to give comparable results in regard to crustal deformation. The UMS models exhibit additional features including single- and double-slab breakoffs and corresponding episodes of uplift and gravitational spreading within the orogenic crust. Protracted postconvergent gravitational spreading of the hot, decoupled crust is also demonstrated. Lastly, we demonstrate the application of this type of model to natural orogens, the Grenville orogen in western Ontario and the southern Canadian Cordillera, and in terms of the T–M diagram.