The sensitive high—resolution ion microprobe (SHRIM P)U—Pb zircon dating of plagiogranite from the Bayingou ophiolite in the northern Tianshan M ountains indicates that the magmatic age of the plagiogranite is 324．8± 7．1Ma (2o)，which shows the Bayingou ophiolite was formed in the early Carboniferous． This suggests the existence of the late Paleozoic“Red Sea type"ocean basin in the northern Tianshan M ountains and the Baiyingou ophiolite is the rem nant of the oceanic crus.