A segmented high Gangdese arc before the India−Eurasia collision from triple oxygen isotope paleoaltimetry

Quantifying the paleoelevation of the Tibetan Plateau is critical for understanding its tectonic evolution, yet direct quantitative constraints on the past elevations of high mountain ranges remain sparse. We applied triple oxygen isotope (Δ′17O) paleoaltimetry to hydrothermal quartz from the Gangdese arc in southern Tibet to reconstruct Late Cretaceous−Paleogene meteoric water composition. Our results indicate that elevations of ∼3.2−4.7 km were already established along the Gangdese arc between ca. 77 Ma and 59 Ma, prior to the India−Eurasia collision. Integrated with previous isotope-based paleoelevation records, our data reveal that the pre-collisional Gangdese evolved as a segmented mountain belt, with elevated and comparatively lower sectors coexisting along strike rather than forming either a laterally uniform arc or a simple east-west topographic gradient. By providing direct constraints on surface elevation, our study offers a revised framework for reconstructing pre-collisional Gangdese topography and demonstrates the value of Δ′17O paleoaltimetry for resolving spatial variations in ancient mountain belts.