The Cretaceous Dagzhuka ophiolite lies in the middle segment of the Yarlung-Zangbo suture zone, Tibet, and has a well-preserved ophiolitic section including a mantle sequence, cumulate complex, diabase dyke swarm and basaltic lavas. Compared to the primitive mantle, tectonized peridotites in the Dagzhuka ophiolite are depleted in Al, Ca, Ti and high field strength elements, but relatively enriched in large ion lithophile elements (Rb, Ba, Th). They have U-shaped, chondrite-normalized REE patterns suggesting an early stage of depletion by partial melting, followed by enrichment from slab-derived fluids. These features support a model in which the mantle peridotites at Dagzhuka formed in a forearc setting. The diabases and basalts are low-K tholeiites depleted in LREE, with compositions similar to N-MORB. However, these rocks are strongly depleted in Nb and Ta but enriched in Th and Rb, features characteristic of island arc lavas. Thus, the Dagzhuka ophiolite is believed to have formed in a supra-subduction zone environment, possibly a fore-arc basin.ophiolite has a well-preserved lithologic sequence ranging from mantle peridotite at the base to pillow lava at the top and thus provides an ideal environment in which to study the evolution of the Tethyan ocean basin (Nicolas et al., 1981;Girardeau et al., 1985;Wang et al., 1987).Although the ophiolite has been studied extensively, there is no agreement as to its origin or tectonic setting. For example, Girardeau et al. (1985) suggested that it formed at mid-oceanic ridge whereas Wang et al. (1999) favored formation in a small, multi-stage oceanic basin. Here we report the results of extensive field and laboratory studies over the past decade and present a new interpretation of the ophiolite. New major and trace element data place important constraints on the tectonic setting of the Dagzhuka ophiolite and suggest that it formed in a supra-subduction zone environment.