The Zedong terrane: a Late Jurassic intra-oceanic magmatic arc within the Yarlung–Tsangpo suture zone, southeastern Tibet

An overturned sequence of igneous and volcaniclastic rocks crops out along the Yarlung–Tsangpo suture zone (YTSZ), in southeastern Tibet. These rocks are remnants of an intra-oceanic island arc, the Zedong terrane, that once lay between India and Asia. 40Ar/39Ar dating and U–Pb ion microprobe analyses reported here reveal that this arc was active during the Jurassic. U–Pb dating of zircon from a dacite breccia from the middle portion of the Zedong terrane, yields an age of 161±2.3 Ma (1σ). 40Ar/39Ar dating of hornblende from a cross-cutting andesite dyke yields the youngest age of 152.2±3.3 Ma (1σ). 40Ar/39Ar results from hornblende from andesite dykes and an andesite breccia from the upper portion yield a mean age of 156±0.3 Ma (1σ). Additional U–Pb and 40Ar/39Ar dating of zircon and hornblende from quartz diorite yields a mean age of 156.8±0.8 Ma (1σ). Geochronological data reported here and other published work indicate that the intra-oceanic subduction system to which the Zedong terrane belonged was active from at least Late Jurassic to Early to mid Cretaceous.