Timing of the Tsergo Ri landslide,Langtang Himal,determined by fission-track dating of pseudotachylyte

Fission-track dating was carried out on zircon grains from pseudotachylyte associated with a Late Pleistocene landslide (Tsergo Ri landslide) in Langtang Himal, Nepal. Zircon grains were separated from an injection pipe of glassy and vesicular pseudotachylyte about 10 cm in diameter. The resulting age of 51±13 Ka lies between the two subpeaks (70 and 20 Ka) of the Würm glacial period, and is concordant with the previous age estimate from geomorphological evidence (i.e. older than 25–30 Ka). This is the first reliable isotopic age for a landslide-generated pseudotachylyte excluding the possibility of contamination by an inherited age.