Description

GA Guide 76

The text of this guide follows the route of a ‘megatransect’ from the Indian Plate across the Himalayan Mountain Range to the Tibetan Plateau on the Eurasian Plate. The transect takes the reader through the Siwaliks of southern Nepal and then on to a section up the Kali Gandaki River of west central Nepal, a tributary of the Ganges River that marks the western side of the Annapurna Circuit trekking route. Here the metamorphic and sedimentary rocks of the Lesser, Greater and Tethyan Himalayan Series can be studied in turn, going northwards. ‘Diversions’ are taken to Mount Manaslu, in Nepal, and to Bhutan to provide better understanding of the leucogranites of the Greater Himalayan Series.
Next, a dogleg in the megatransect takes the reader to Ladakh where volcanic and deep-water sedimentary rocks of the Indus Tsangpo Suture Zone can be seen together with evidence of deep burial down a subduction zone. Onward then to look at Tibetan terranes on the Eurasian Plate, where granitic batholiths are well exposed. Syn- and post-collisional molasse can be studied in Ladakh’s Indus Basin, lying over the Indus Tsangpo Suture Zone.
A ‘leap’ south-eastwards to study comparable Oligo-Miocene conglomerates goes along the suture to the sacred Mount Kailas, thereby completing the megatransect. There is also a diversion to examine Quaternary sediments in the Kali Gandaki valley and another to look at the evolution of the four holy rivers: the Indus, the Yarlung-Tsangpo-Brahmaputra, the Sutlej and the Ganges. At each stage of the megatransect there is a brief explanation of the processes involved (e.g. metamorphism, plate tectonics) for non-specialists.