Evidence for rapid displacement on Himalayan normal faults and the importance of tectonic denudation in the evolution of mountain ranges

East-striking, low-angle normal faults of the South Tibetan detachment system have played an important role in exposing the high-grade metamorphic core of the Himalayan orogen. In the Mount Everest region of southern Tibet, granites both pre- and postdate an important fault of the system, the Qomolangma detachment. New U-Pb and ⁴⁰ Ar/ ³⁹ Ar geochronologic data for these rocks constrain the age of brittle faulting to between 16.67±0.04 and 16.37±0.40 Ma, significantly expanding the known age range for extension in the central Himalaya (widely regarded as c20-22 Ma). More importantly, they indicate an average displacement rate of ≫47 mm/yr and a consequent tectonic unroofing rate of ≫8.2 mm/yr. Such unroofing is faster than all but the highest estimates of combined physical and chemical erosion rates in mountainous regions, suggesting that large-displacement normal faulting can be an extremely efficient agent of mass redistribution of orogenic systems.