The metamorphic and magmatic record of collisional orogens

The Cenozoic Himalaya-Tibet orogen is generally regarded as the archetypal continental collision zone and is often used as an analogue for interpreting ancient orogenic events. However, given the wide diversity observed in present-day collisional mountain belts, the extent to which such inferences can be made remains debated. In this Review, we compare the metamorphic and magmatic record of the Himalaya-Tibet orogen to four ancient orogens — the Palaeozoic Caledonian orogen, the Meso-Neoproterozoic Grenville and Sveconorwegian orogens, and the Palaeoproterozoic Trans-Hudson orogen — to establish the controls on the underlying dynamics and the nature of the resulting rock record. The similarities in rock records, and, thus, thermal conditions, are interpreted to result from comparable foreland strengths, resulting in similar maximum crustal thicknesses. Apparent differences in the records are mainly attributed to variation in exposed structural level rather than fundamentally different tectonic processes. We, therefore, suggest that foreland rheology is a critical factor in determining the effectiveness of orogen comparisons. Future research is required to investigate the causes and consequences of lateral variability in mountain belts, in particular, focussing on the record of orogens smaller than those considered here, and to understand if and why mountain building processes have varied through Earth history.