Eastern Tianshan late Paleozoic volcanic zone is located at the center of the Paleo-Asian Oceanic Belt. A number of small tonalitic, trondhjemitic and granodioritic plutons occur in this volcanic zone, among which 6 typical plutons were selected to study their geochemical features and petrogenesis. These plutonic rocks are characterized by high Na(2), O, Al(2)O(3), and Sr contents, low Y and HREE contents and high Sr/Y and La/Yb ratios, similar to the modem adakite. These rocks also possess positive epsilon(Nd) (T) ( + 1. 80 similar to + 8.47) and very low initial (87)Sr/(86)Sr (0. 7026 similar to 0. 7051). These Nd and Sr isotopic compositions are also similar or close to those of most subduction-related adakites which have like-MORB isotopic compositions. The above geochemical and isotopic features, in conjunction with late Paleozoic subduction setting, suggest that these adakitic rocks may be produced by partial melting of the subducted Zhungaer oceanic crust during late Paleozoic. The MORB ( basaltic oceanic crust) are a very important source for adakitic rocks and contain high abundance of Cu, An and volatile components H(2)O and Cl etc. The large scale of decomposition of amphibole within the subducted oceanic crust during the generation of adakite magmas will release large amount of H,O, Cl and Cu, An into the magmas. The rapid decrease of pressure during ascent of the magma will cause release of Cu, An and volatiles to form ore-forming fluid. During the entire process from magmatic production through magmatic transportation and interaction with mantle wedge to the final stage of fluid release from the magma, high oxygen fugacity (fo(2)) is necessary, which will restrain the stability of sulphides to make Cu, An enriched in the magma. Eastern Tianshan area has become an important exploration target for industrial Cu deposits due to the discovery of the superlarge Tuwu-Yandong porphyry Cu deposit whose parent magmas are adakitic rocks. The newly reported adakitic rocks here are surely helpful for the guidance of further exploration of similar Cu, An deposits in this area.
