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 (1sigma). 40Ar/39Ar dating of homblende from a cross-cutting andesite dyke yields the youngest age of 152.2 +/- 3.3 Ma (1sigma). 40Ar/39Ar results from homblende from andesite dykes and an andesite breccia from the upper portion yield a mean age of 156 03 Ma (1sigma). Additional U-Pb and 40Ar/39Ar dating of zircon and homblende from quartz diorite yields a mean age of 156.8 +/- 0.8 Ma (1sigma). 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. (C) 2002 Published by Elsevier Science B.V.