【摘要】 蛇绿岩中的辉绿岩岩墙是洋脊扩张的产物,其形成年龄代表了扩张事件的时间,也代表了蛇绿岩的形成时代。对雅鲁藏布江缝合带中段桑桑蛇绿岩中的辉绿岩岩墙进行了SHRIMP锆石U-Pb定年,得出加权平均年龄为(125.2±3.4)Ma(2σ,MSWD=1.15),即辉绿岩结晶年龄。结合已有的关于雅鲁藏布江蛇绿岩形成年龄(中段大竹卡(126.0±1.5)Ma,吉定(123.0±1.8)Ma;西段休古嘎布(122.3±2.4)Ma和东段罗布莎(162.9±2.8)Ma)的报道,该结果表明桑桑地区特提斯洋海底扩张的时代,与中段大竹卡、吉定地区以及西段休古嘎布地区洋盆形成时代一致,但晚于东段发育时代,表明雅鲁藏布江缝合带中段地区洋盆时代相当,而整个东特提斯洋盆发育时代存在东早西晚的特点。更多还原

【Abstract】 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 Géding 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 Géding 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.更多还原