Non-progressive orogenesis of the Southern Tibetan Plateau

The Lhasa Terrane (LT), a ∼2000-km-long orogenic belt within the Neo-Tethyan tectonic domain, constitutes the southern Tibetan Plateau (STP). Geochronological data reveal non-progressive (multi-phase) surface uplift, initiating in the central LT rather than the southern LT adjacent to the collisional front. To resolve the geodynamic drivers of this uplift pattern, we present an integrated analysis of a 345-km-long N-S deep seismic reflection profile traversing the entire LT. This unified transect reveals a critical structural continuity invisible to isolated studies: the non-reflective crust in the southern LT transitions to a continuous north-dipping crystalline basement wedge that tapers progressively northward from the central to northern LT. Integration of multi-disciplinary data with geodynamic modeling supports a three-phase orogenic evolution, suggesting that while the evolving Neo-Tethyan slab dynamics and subsequent Indian collision provided the external geodynamic drivers, the inherited across-strike crustal strength heterogeneity acted as the internal template. Initially, early-stage subduction induced northward basement tilting and early uplift. Subsequently, slab rollback (<70 Ma) drove juvenile crustal accretion and magmatic softening in the southern LT, causing delayed uplift upon Indian indentation. Finally, Late Oligocene-Miocene passive roof thrust systems modified the relief. These validated processes demonstrate that external tectonic forcing interacted with inherited crustal structures to fundamentally affect the spatial progression of thickening, thereby establishing the STP's non-progressive orogenic framework.