Abstract: A hot mantle plume,i.e.the one in between of continental rift and oceanic spreading,indicated by geochemical data,was developed during Sinian to Early Ordovician in Kuruktag area of the Tarim Basin.The Sinian volcanics are typical bimodal volcanic rocks in Kuruktag area,which are consisted of acidic and basic volcanic rocks but with rare medium acidic one.REE distributive pattern of basic volcanic rocks showed steep right dip and was rich in light REE which is in accordance with REE geochmical characters of basalt from mantle plume.In the northeast of Tarim Basin,depositional facies were arranged as basinal,slope,platform margin and restricted-open platform facies from east to west in Cambrian to Ordovician,which showed the sedimentation of passive continental margin.Therefore,the Kuruktag ur-ocean rift and Manjaer original continental margin were proposed.There is potential for petroleum exploration around the Manjaer original continental margin.