Alkali-rich porphyry and its relation with intraplate deformation of north part of Jinsha River belt in western Yunnan, China

A suite of alkali rich porphyry with 26.5\37.6Ma occur along the Jinsha River suture zone in west Yunnan. They are characterized by LREE rich distribution patterns and no Eu anomaly. These porphyries have formed in post collisional environment; （ 87 Sr/ 86 Sr） i of porphyries, amphibolite xenolithes and associated basalts are 0.707 3, 0.706 5\0.707 1 and 0.705 8\0.706 5, ε Nd （ T ） are -3.4\-6.3, -2.1\-7.4 and -3.3 respectively. Pb isotope compositions of these rocks also show a little difference. The evidence shows that the porphyry could be derived from partial melting of the "crust mantle mixed layer". The relation between Cenozoic magmatism and intraplate deformation since Paleogene has been discussed.