Back folds in the core of the Himalayan orogen: An alternative interpretation

The hanging wall of the South Tibetan detachment system in the central Nepa l Himalaya is characterized by regional-scale, northeast-verging folds, cla ssically interpreted as gravity-induced structures developed during down-to -the-north extensional shearing along the detachment system. New structural observations and balanced cross sections of the Tethyan sedimentary sequen ce in the Kali Gandaki area and new U-Pb geochronology support an alternati ve interpretation. The northeast-verging folds developed before ductile ext ensional shearing along the detachment system, thereby recording some of th e earliest contraction of this part of the orogen. We propose a new model i n which the northeast-verging folds of the Kali Gandaki area represent the northern part of a late Eocene to Oligocene contractional fan structure.