Abstract

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 40Ar/39Ar 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 ca. 20–22 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 in orogenic systems.

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