Nanga Parbat - an uplifting tale - by Mike Searle
Mike Searle reflects on Wadia’s Nanga Parbat work in the light of modern discoveries.
Darashaw Nosherwan Wadia was a field geologist in the great tradition of early 20th Century observation-driven exploration geology. As Geoff Glasby explains, he mapped thousands of square miles for the Geological Survey of India throughout Kashmir, particularly in the provinces of Poonch, Chilas and Gilgit. His ‘adventure treks’ for students took him into the remotest corners of Kashmir. In the days of pre-1947 partition of India and Pakistan, he roamed through much of what is now the disputed border region along the Kashmir cease-fire line. Due to the numerous conflicts and border wars in Kashmir since independence, many of the regions that he explored and mapped have not subsequently been visited by geologists, to this day. Wadia had widespread interests, his work ranging from Pleistocene fossils in the Siwalik molasse to the Archean basement gneisses.
Wadia was the first to identify the great Western ‘Syntaxis’ of the Himalaya or the ‘Nanga Parbat bend’, where a great tongue-like projection of lower crust gneisses projected north of the main Himalayan axis. Wadia’s ‘Geological Map of Part of the Gilgit District’ at a scale of one inch to four miles included all the territory around the peak of Nanga Parbat (8125 metres). This work included the first cross-section across the Nanga Parbat massif from the Indus valley in the west to the Rupal glacier in the east. Wadia recognized that the massif was composed of gneiss with interbedded ‘Salkalla Series’ surrounding a central summit region composed of ‘granitoid gneiss’. He assumed, quite reasonably for the time, that these crystalline rocks were part of the Archean basement of India.
Wadia would be amused to know that now, the Nanga Parbat gneisses show the youngest metamorphic event dated by U-Th-Pb anywhere in the world! These Precambrian basement gneisses and migmatites have tourmaline, garnet and sillimanite-bearing granite melts with U-Pb monazite, xenotime and zircon ages ~900 ka, and some cordierite and tourmaline bearing melts as young as 700,000 years. Cordierite-bearing leucogranite seams and veins record Pleistocene crustal melting at depths of ~17-10km. Exhumation (uplift of rock) rates of about 13mm/year in the core of Nanga Parbat are phenomenally high for continental crust. Leucogranitic rocks that now form the summit region of Nanga Parbat massif were formed by high-temperature biotite dehydration melting of Precambrian crust at depths of ~17-10km beneath the Earth’s surface.
Wadia’s legacy to Himalayan geology is unique and spectacular. His book Geology of India 11 , published in 1919 and reprinted six times, is still widely used to this day. He was undoubtedly one the greatest of Indian geologists, whose name lives on in the Wadia Institute of Himalayan Geology in Dehra Dun, renamed in his honour from the Indian Institute of Himalayan Geology, which he founded. His name will always be intimately linked to the snows of Nanga Parbat, surely one of the most spectacular of all Himalayan mountains.