Understanding the uplift history of the Tibetan Plateau is key to grasping the geodynamic processes that formed the "Roof of the World," as well as its far-reaching impacts on regional and global climate and the evolution of Asian biodiversity. The Gangdese Mountains, which run along the southern margin of the Lhasa terrane, are central to this story and among the many topographic features of the plateau.

In a study published in Earth and Planetary Science Letters on August 8, researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences and their collaborators have for the first time quantitatively confirmed a rapid rise of the Gangdese Mountains in southern Tibet around 15 million years ago. They demonstrated that the range's peaks soared to over 6 kilometers (3.7 miles) above sea level, roughly 1.5–2 kilometers (0.9–1.2 miles) higher than today's elevation of about 4.5 kilometers (2.8 miles).

To reconstruct this ancient event, the researchers combined fossil pollen and spore analysis, macrofossil records, and high-resolution climate-vegetation models. By examining pollen assemblages from the Namling Basin in southern Tibet, they detected a sharp and abrupt ecological transition: a temperate–subalpine forest ecosystem gave way to alpine shrubland and shrub-meadow within a short geological timeframe.

"This was not a gradual change driven by global climatic trends, but a local, catastrophic event that fundamentally reshaped the environment," said LI Shufeng of XTBG.

Their modeling revealed that a rapid surface uplift of 525 to 1,050 meters was necessary to explain the observed vegetation shift. This would have pushed the basin floor to an elevation exceeding 6 km, which is substantially higher than its present-day position.

While the Namling area rose sharply, contemporaneous pollen records from the central Tibetan Plateau (Lunpola Basin) show no such shift in vegetation. This suggests that the 15-million-year-old uplift did not affect the entire Gangdese chain uniformly, likely due to east-west variations in Indian plate subduction and slab break-off.

The researchers propose that the subsequent, post-15-million-year decline in elevation was driven by two major tectonic forces. The first is the continued subduction of the Indian Plate beneath the Eurasian Plate, which created a downward drag on the southern Lhasa terrane. The second is the late Cenozoic, east-west extensional collapse of the southern Tibetan Plateau.

"Our work demonstrates that, when combined with climate modeling, pollen can serve as a powerful altimeter for ancient landscapes," said LI Shufeng.