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U-Pb age and Hf-O isotope data of zircons from the mafic-ultramafic complexes and their related rhyolites and granites in the Eastern Tianshan and Beishan regions were obtained by SIMS and LA-ICPMS.The Hf-O isotopic composition and Hf model age of the zircons are closely related to their tectonic setting and formation age.The zircons from the mafic-ultramafic complexes in the Bogeda-Haerlike and Jueluotage belts have higherε_(Hf)(t) (+ 8-+ 17) and lowerδ~(18)O(+ 4‰- + 6‰),whereas most of the zircons in the gabbros,granites and rhyolite from the Middle Tianshan Massif and Beishan Rift display lowerε_(Hf)(t)(0- + 8) and higherδ~(18)O(+ 5‰- + 8‰). The positiveε_(Hf)(t) and relatively lowerδ~(18)O values suggest that these mafic-ultramafic complexes were derived from depleted mantle whic