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��