Abstract: Isotopic age determination on the Susong Group metamorphic rocks yields Rb-Sr whole-rock isochron ages of 448 Ma and 470 Ma, a Rb-Sr whole rock- mineral isochron age of 231 Ma and a phengite K-Ar age of 210 Ma. The results show that for the Susong Group folding and metamorphism occurred in the Caledonian movement and that compresso-shear took place in the Indosinian Cycle. The rocks exhibit well-developed schistosity and gravels in fractures are plastically deformed to assume a "S" shape, so the rocks appear to be both ductile and brittle. Petrological and isotope chronological studies show that the nappe structure of the Susong Group were formed during the Indosinian period.