中文摘要：

报道了江南造山带（中-）西段在＂俯冲造山阶段＂形成的科马提质玄武岩、石英角斑岩、流纹质凝灰岩及＂后造山伸展阶段＂形成的两类基性岩的特征,研究表明,科马提质玄武岩是形成于岛弧环境的高MgO玄武岩。高的Ni和Cr含量说明它们为来自弧下地幔的原始岩浆,较高的MgO显示这些高MgO玄武岩浆是在相对较干的条件下从地幔源区分离的。＂后造山伸展阶段＂形成的两种基性岩分别来自软流圈和岩石圈地幔,具有不同的地球化学特征。基底地层中砂岩的碎屑锆石及夹层中基性—酸性火山岩的锆石U-Pb定年表明,在扬子板块东南缘,新元古代岛弧岩浆活动的时间约为878～822Ma,岛弧地区陆源碎屑的沉积作用发生在872～835Ma期间,表明存在同时代的（coeval）＂岛弧岩浆作用＂和＂沉积作用＂。

英文摘要：

The characteristics of the komatiitic basalts, quartz-keratophyre and rhyolitic tuff formed in the subducted stages of the oceanic crust as well as the two kinds of basic rocks formed in the post-orogenic extensional stage in the development of the （middle-） western Jiangnan orogen are reported in the paper. The kamatiitic basalts are considered to be the high-MgO basahs formed in island-arc settings. Their high Ni and Cr contents suggest that they were the primary basalts derived from the sub-arc mantle. Their high MgO contents indicate that the basaltic magmas were extracted from its mantle source under relatively dry conditions. The two subtypes of the mafic rocks formed in the post-orogenic extensional stage might be derived from the partial melting of the asthenospherie and lithospheric mantles, respectively, and show contrasting geochemical features. U-Pb zircon dating data for samples of the mafic and acidic rocks as well as sandstones hosted in the Neoproterozoic basement strata in the western Jiangnan orogen reveal that deposition of the terrigenous fragments in the island-arc area took place between 872 Ma and 835 Ma. The magmatism with arc signatures occurred from 878 Ma to 822 Ma. Therefore, we believe that there existed coeval arc magmatism and sedimentation along the southeastern margin of the Yangtze Block during the Neoproterozoic.