1． College of Earth Sciences，Jilin University，Changchun 130061，China; 2． Institute of Geology，Chinese Academy of Geological Sciences，Beijing 100037，China

The Nadingcuo volcanic rock suite is the most voluminous Cenozoic volcanic suite in the southern Qiangtang area of the northern Tibetan Plateau． These high- K calc- alkaline volcanic rocks were formed between 36 and 34 Ma，characterized by high Mg # values，high concentrations of TiO 2 and P 2 O 5 ， 87 Sr/ 86 Sr ratios of 0． 704682- - 0． 706 112，and εNd(t) values of －1． 2 to 1． 6． There is a lack of reasonable explanations for sour- cing and origin of magmas that formed the rocks with high Mg # values and TiO 2 and P 2 O 5 enrichments，which makes the previous research results still controversial． This study reviews the geochemical characteristics of Nadingcuo volcanic rocks and the data we have newly found in our fieldwork． We give some new interpretation to the magmatic evolution of the basaltic magmas in the discussed area dominated by fractional crystallization． The geochemistry of trachyandesite and trachyte units in the studied area is indicative of formation from mantle- derived magmas that mixed with crustal materials． The high values of Mg # and TiO 2 and P 2 O 5 enrichment in these units are evident to show the mixing between mantle- derived magmas with ～30- - 40 wt．% rhyolitic melt or assimilation of a similar amount of felsic rocks． The geochemistry of basaltic rocks in the area also suggests that the Nadingcuo basalts may have been derived from an ocean island basalt (OIB)- type source that contained and was mixed with ancient mantle wedge derived material，indicating that a 36- - 34 Ma asthenospheric upwelling e- vent in the Qiangtang area may relate to the northward subduction of Indian lithospheric mantle and the south- ward subduction of Asian lithospheric mantle． This upwelling of asthenospheric material was centered in the southern Qiangtang area between 36 and 34 Ma， while the northward movement of the Indian Craton caused this upwelling mantle flow to continuously migrate northward，resulting in the current centering of this upwelling in the Hoh Xil- Kunlun region．