SHRIMP U-Pb dating for diabase in Sangsang ophiolite,Xizang,China:Geochronological constraint for development of eastern Tethys basin

As the product of the middle ocean ridge extension,the diabasic dykes in ophiolite possess a formation age corresponding to the extension time,and this age also represents the formation time of the ophiolite.In this paper,zircon SHRIMP U-Pb technique was applied to the diabasic dykes in the Sangsang ophiolite,middle part of the Yarlung Zangbo suture zone,Xizang(Tibet),China.A 206Pb/238U mean age of(125.2±3.4)Ma(2σ,MSWD=1.15)was obtained,which is also the formation time of the diabase.Compared with the former reported ophiolite ages in the Yarlung Zangbo suture zone((126.0±1.5)Ma for the Dagzhuka ophioilte and(123.0±1.8)Ma for the Geding ophiolite in the middle part,(122.3±2.4)Ma for the Xiugugabu ophiolite in the western part and(162.9±2.8)Ma for the Luobusha ophiolite in the eastern part),this age also suggests that the extension time of the Tethys oceanic basin in Sangsang region was consistent with the formation time of the Dagzhuka and Geding oceanic basin in the middle part,and also corresponding to that of the Xiugugabu oceanic basin in the western part,while later than the development of Luobusha oceanic basin in the eastern part of the Yarlung Zangbo suture zone.From the geochronology data,it can be deduced that the development of the oceanic basin in the middle part of the Yarlung Zangbo suture zone was synchronized,while the open time of the eastern Tethys basin was characterized by being gradually later from east to west.