A continental collision zone
The Yarlung Tsangpo Suture Zone marks the geological seam where the drifting Indian subcontinent crashed into Eurasia. This continental collision, which began between 52 and 50 million years ago, closed the ancient Neo-Tethys Ocean that once separated the landmasses. Before the impact, the Indian Plate moved northwards at a record-breaking speed for a tectonic plate, reaching about 15 centimeters per year. After making contact, its advance slowed by about half.
The immense pressure of the two continental plates pressing against each other caused the crust to buckle and thicken dramatically, giving rise to the Himalayan mountain range and the vast, high-altitude Tibetan Plateau. The plateau now has an average elevation exceeding 4,500 meters and covers an area of 2.5 million square kilometers. Running parallel to the suture zone is the Gangdese batholith, a massive body of granite and other igneous rocks over 1,500 kilometers long. It is the remnant of a volcanic arc that was active on the southern edge of Asia before and during the collision. A major magmatic flare-up in the Gangdese arc between 55 and 45 million years ago shows the arrival of the Indian plate.
Remnants of a lost ocean
The most direct evidence of the former Neo-Tethys Ocean lies within the suture zone itself, in the form of ophiolites. Ophiolites are sequences of rock that represent a cross-section of oceanic crust and the underlying upper mantle that have been scraped off and thrust onto a continental plate. The Yarlung Tsangpo ophiolites are distributed discontinuously for nearly 2,000 kilometers along the suture.
These geological assemblages contain specific rock types that form in deep marine environments. They feature mantle peridotites like harzburgite and lherzolite, which formed the base of the oceanic lithosphere. Above these are gabbros, which cooled slowly in magma chambers beneath the ocean floor, and dolerite dikes. The sequence is topped by pillow lavas—basalts that erupted underwater and cooled rapidly into distinctive bulbous shapes. The presence of these complete ophiolite suites shows the oceanic crust that was almost entirely consumed through subduction as India moved north.