Abstract:

A set of Tertiary alkali—rich porphyries occurs in the Jinshajiang River—Ailao Mountain fault belt，western Yunnan Province. And many types of deep—derived xenoliths have been discovered in some of the alkali—rich porphyries. Research on the porphyries and xenoliths is very important for understanding the composition and evolution of the mantle and the interaction between the mantIe and the crust in western Yunnan. In this paper，rock types and petrographic characteristics of the porphyries and xenoliths in Liuhe，Xinhua，Dianxin and Xiaoqiaotou are introduced and the analysis results of major elements，trace elements，rare earth elements and Pb-Sr-Nd isotopes are presented．Based on these analyses，geochemical discrimination diagrams and studies of experimental petrology and phase equilibrium，the followirlg conclusions have been
reached：Most of the alkali-rich porphyries are shoshonitic and formed in post-collision arc settings；magmas of alkali—rich porphyries originated near the bottom(about 55 km in depth)of the thickened crust in western Yunnan；the source rocks may be those of eclogite phase；the geochemical characteristics of EMⅡenriched mantle in the source region is likely related to the mixing of the lower crust and the mantle with fingerprints of subducted ocean crust．

Key words: westernYunnan, alkali—rich porphyry, deep—derived xenolith, shoshonite, geochemistry, crust-mantle interaction, petrogenesis