Plate Tectonics

Chapter 13 deals with the ultimate stage of plate convergence, which is continent-continent collision. Collisional orogeny starts when an ocean is closed and two continental margins collides. Structures, processes and evolution of collisional mountain belts are covered from a general perspective, and different types of such orogens are outlined. Asymmetric versus symmetric belts are explained, and the overall structure of an orogenic belt, from the non-metamorphic foreland to the high-grade hinterland or core. The chapter explores foreland basins and foreland thrusting-related structures such as duplexes and detachment folds, and how deformed foreland layers can be restored to explore orogenic displacements involved. It explains why the hinterland heats up as crustal thickening continues or is maintained, and how this can enhance mid-crustal flow and orogenic plateau formation. Continental subduction is also discussed, where one of the continental margins is pulled down to sub-crustal depths and ultra-high pressures. Models for exhumation of (ultra)high-pressure rocks and the channel flow model are discussed, as is the role of syn- to postorogenic extension. The chapter also covers intracontinental orogeny, where no ocean is involved, and covers erosional aspects of continental orogens.