A geological journey through the deepest gorge on Earth: the Kali Gandaki valley section, west-central Nepal

The Kali Gandaki valley in the Central Himalaya is flanked by the eight thousand meter high Annapurna and Dhaulagiri massifs forming the deepest gorge in the world. It offers an invaluable opportunity to directly observe a cross section through the continental crust involved in the Himalayan orogen. The northsouth trend of the valley runs almost perpendicular to the dominant regional strike and cross cuts the major tectonic units that comprise the Himalaya including the Lesser Himalayan Sequence, the Greater Himalayan Sequence and the Tethyan Sedimentary Sequence. The valley is easily accessible compared to many other sections across the belt and its history as a popular trekking route ensures services and lodging that are often not available elsewhere. We propose a one-week itinerary across the low metamorphic grade Proterozoic quartzites of the Lesser Himalayan Sequence in the south, through the high-grade, migmatitic metamorphic core of the Greater Himalayan Sequence to the unmetamorphosed Cretaceous age sedimentary rocks of the Tethyan Sedimentary Sequence to the north. This line of section allows observation of major, orogenic-scale tectonic faults/shear zones such as the Main Central Thrust and the South Tibetan Detachment, which bound the bottom and top of the high-grade core respectively, as well as other important shear zones within the Greater Himalayan Sequence (i.e. Kalopani shear zone). The Kali Gandaki section also offers spectacular examples of both mesoscopic and mountain-scale deformation structures including km-scale north-verging folds within the Tethyan Sedimentary Sequence.