The widespread Cenozoic magmatism in the Red RiverAilaoshan tectonic zone is closely related to the IndianEurasian plate collision orogeny. Zircon UPb dating results of two granitic samples exposed in the middle part of the Ailaoshan metamorphic belt are 26.2 ± 0.5 Ma and 26.8 ± 0.5 Ma

respectively. This indicates that the Ailaoshan metamorphic zone is not entirely attributed to the Proterozoic crystalline basement of the Yangtze block

while it also contains Cenozoic magmatic rocks. Zircon ε

Hf

(t)values of the samples range from +0.3 to +6.9 and from -9.8 to -0.7 with mean values of +3.4 and -4.3

respectively and their corresponding twostage Hf model ages T

DM2

range from 526 to 853 Ma and from 903 to 1 355 Ma. The high ε

Hf

(t) granites were derived from partial melting of juvenile crust induced by the asthenospheric mantle heat source

while low ε

Hf

(t) granites from Proterozoic metamorphic sandstones of the Ailaoshan group. In combination with previous research results

we suggest that the Red River fault has cut across the lithosphere mantle. In SE Asia

the Gaoligongshan and Ailaoshan strikeslip shear zones on both sides of Indosinian block dismembered different blocks and created conditions for their Oligocene extrusion to the southeast.