Abstract:
The Altai orogen (northwest China) represents the southwestern margin of the Central Asian Orogenic Belt. Geochemical and Nd3.4 to 1.8 Ga, and ISr = 0.7106 to 0) and ISr (0.7110.7051). Voluminous syn-orogenic granitoids have [varepsilon]Nd(T) = +2.1 to 0.714 and TDM = 0.7–1.6 Ga. They were not derived by melting of local metasedimentary rocks as suggested by previous workers, but by melting of a more juvenile source at depth. Post-orogenic granites have higher [varepsilon]Nd(T) ([similar] +4.4) than the syn-orogenic granitoids, indicating their derivation from a deeper crustal level where juvenile crust may predominate.
