扬子地块南缘晚古生代洋壳存在的Nd同位素证据

The Nd Isotopic Evidence for Late Paleozoic Oceanic Crust in Southern Margin of Yangtze Block

总结我国扬子地块南缘新元古代—早中生代沉积岩目前已发表的Ｎｄ同位素资料发现，这些沉积岩具有随时间变化而其Ｎｄ同位素组成发生漂移的现象。在绝大多数时间里，它们具有２０００Ｍａ左右的Ｎｄ模式年龄，但在１０００～７００Ｍａ的新元古代和＜４００Ｍａ的晚古生代—早中生代时间段中，Ｎｄ同位素模式年龄急剧降低，反映在此时间段内，新生地幔物质已经进入沉积物的物源区。１０００～７００Ｍａ期间的Ｎｄ同位素变化归因于晋宁期的碰撞造山作用而晚古生代－早中生代沉积岩的Ｎｄ同位素变异起因于海盆发育阶段洋壳的出现。即扬子地块南缘在晚古生代—早中生代期间曾经存在过洋壳，且该洋盆可能是古特提斯大洋分支的一部分。

The systematic Nd isotopic analysis of Neo Proterozoic Early Mesozoic sedimentary rocks from Southern margin of Yangtze Block show that these rocks have the feature of Nd isotopic shift with their ages. In most of their deposit time, these rocks have Nd model age of about 2000Ma.However, at stages of 1000-700Ma and <400Ma, the Nd model age decreased rapidly, which suggests that the juvenile mantle derived material had become one of the source components of these sedimentary rocks. The variation of Nd isotope in sedimentary rocks of 1000￣700Ma resulted from the Jinning orogenesis and that of Late Plaeozoic Early Mesozoic originated from the newly developed oceanic crust, which could be one of the branches of Plaeo Tethys Ocean.