The Cenozoic evolution of the Himalaya-Tibet Plateau, dictated by the
India-Asia convergence, remains a subject of substantial ambiguity.
Here, a thermo-mechanical model is used to show the critical controls of
decelerating convergence on the formation and stabilization of
distinctive tectonic structures during prolonged collision. At high
constant convergence rates, similar to the late Paleogene India-Asia
motions, the lower plate crust is injected beneath the overriding crust,
uplifting a plateau, first, then is exhumed towards the orogeny front.
Conversely, low constant convergence rates, similar to the Neogene
India-Asia motions, induce crustal thickening and plateau formation
without underplating or exhumation of incoming crust. Strikingly, models
simulating the decelerating India-Asia convergence history portray a
dynamic evolution, highlighting the transitory nature of features under
decreasing convergence, as the orogen shifts to a new equilibrium. In
the transitional phase, the slowing of convergence decreases basal
shearing and compression, leading to extension and heating in the orogen
interiors. This allows diapiric ascent of buried crust and plateau
collapse, as accretion migrates to a frontal fold-and-thrust belt. The
models provide insights into the multi-stage evolution of the long-lived
Himalayan-Tibetan orogeny, from fast early growth of the Tibetan
Plateau, through its transient destabilisation and late-stage internal
extension, behind the expanding Himalayan belt.