Chapter Nine Basins in a Context of Plate Collision

Abstract

This chapter describes the structure, tectonics, and sedimentation of collision areas. The chapter summarizes the closure of the Tethys and collision in the Alps. Collision events may involve continental as well as oceanic lithospheres, and active island arcs as well as active continental margins. In most cases, however, lithospheric plates include areas of oceanic and continental lithospheres, and plate convergence is accommodated through the subduction of oceanic lithosphere beneath continental lithosphere in active margin areas. When the oceanic lithosphere is completely subducted, the continental lithosphere engages within the subduction plane but resists entrainment, because of its low density and important thickness. Internal stress being still transmitted to plate boundaries, convergence is accommodated via thrusting, reverse faulting, and folding, progressively building a collision prism. For example, northward migration of India as the Indian Ocean opened, was initially associated to rapid subduction of Eurasian oceanic lithosphere and reduction of the Tethys Ocean. During collision events, the converging lithospheres are shortened and thickened. The deformation principally affects the underlying (previously subducted) lithospheric plate. Deep seismic investigations in the Western Alps suggest that deformation involves the upper lithospheric mantle in the inner parts of the collision prism (lithospheric prism) toward the overriding plate, the continental crust in the central part of the collision prism (crustal prism), and the sediment series only in the outer collision prism (sedimentary prism) toward the incoming plate.