Slowing Convergence Controls on Orogeny: A Three‐Stage Evolution of the Cenozoic India‐Asia Collision

Abstract The Cenozoic India‐Asia convergence represents the most well‐documented case of long‐lived orogeny, characterized by slowing plate convergence and complex deformation across the collisional margin, from crustal burial, exhumation and thrusting in the Himalaya, to thickening of southern Tibet. Here, we use a thermo‐mechanical computational model to show the controls of decelerating convergence on the lithospheric and orogenic structures during prolonged collision. Constant convergence velocity models, bracketing the India‐Asia convergence velocity, illustrate two rheological end‐members, a fast‐convergence orogeny dominated by lithospheric underthrusting and crustal burial and exhumation, and a slow convergence orogeny dominated by fold‐and‐thrusting and no lithospheric underthrusting. In contrast, models simulating the decelerating India‐Asia convergence history show a unique evolutionary path. The initial structures formed at fast convergence are subsequently destabilized as convergence decreases below ∼5 cm yr −1 , and the structural style transitions from crustal burial and exhumation, and thickening to outwards compression along a frontal fold‐and‐thrust belt, progressively underthrusted by the subducting lithosphere. As the convergence decreases below ∼3 cm yr −1 , the reduced compression cannot sustain the plateau height and crustal thickness, inducing collapse of the orogen interiors and the diapiric ascent of buried crust. These models show a three‐stage orogeny: fast thickening with crustal exhumation, widening along a frontal and fold‐and‐thrust belt, and internal collapse and extension. Similar to structuring of the Himalaya‐southern Tibet, with the early rise of the southern Tibetan Plateau to the Himalayan crystallines formation, to the later thrust belt expansion and internal doming, reconcile with the three‐stages orogeny, emphasizing the role of slowing convergence on orogenies.