Tectonic indicators of continental collision in mountain ranges
A sequence to better understand how certain tectonic features present in mountain ranges attest to collision in a context of lithospheric convergence.
Divergent forces can affect the continental lithosphere. This causes it to stretch, resulting in thinning accompanied by tectonic structures symptomatic of divergence, such as the normal faults that structure the geometry of the tilted blocks characteristic of a continental rift. When divergence continues, the rupture of the continental lithosphere leads to the formation of oceanic lithosphere. This plate divergence implies convergence in other parts of the globe. Lithospheric convergence initially manifests as the subduction of oceanic lithosphere beneath another lithosphere, either oceanic or continental. The disappearance of the oceanic domain leads to a de facto convergence of the two continental margins that bordered the ocean. When the entire oceanic domain has disappeared, the two continental margins collide. This collision is accompanied by characteristic deformations, which we will discuss here: What are the tectonic indicators that attest to a continental collision?
A collision zone is marked by the suture that occurs at the level of the two continental margins that collided. This collision results in a thickening of the continental crust due to stacking related to lithospheric shortening. The first tectonic indicators correspond to the numerous reverse faults that structure the collision zones. At these reverse faults, we observe a relative movement of geological elements in which one block rises above another. On a larger scale, we speak of thrust faults of one geological unit over another or nappes. Finally, compressive forces are also responsible for folds. The emplacement of these tectonic structures, which is accompanied by stacking, is responsible for a thickening of the continental crust. Collision zones are then marked by the existence of a positive relief on the surface associated with a mountain range called a collision chain and a crustal root at depth.