Tectonic implications of U-PL zircon ages of the Himalayan orogenic belt in Nepal

Metasedimentary rocks of the Greater Himalaya are traditionally viewed as I ndian shield basement that has been thrust southward onto Lesser Himalayan sedimentary rocks during the Cenozoic collision of India and Eurasia, Ages determined from radioactive decay of uranium to lead in zircon grains from Nepal suggest that Greater Himalayan protoliths were shed from the northern end of the East African orogen during the Late Proterozoic pan-African oro genic event, These rocks were accreted onto northern Gondwana and intruded by crustal melts during Cambrian-Ordovician time. Our data suggest that the Main Central thrust may have a large amount of pre-Tertiary displacement, that structural restorations placing Greater Himalayan rocks below Lesser H imalayan rocks at the onset of Cenozoic orogenesis are flawed, and that som e metamorphism of Greater Himalayan rocks may have occurred during early Pa leozoic time.