THE Rb-Sr AGES OF METAMORPHIC SERIES OF THE SUSONG GROUP AT THE SOUTHEASTERN FOOT OF THE DABIE MOUNTAINS, ANHUI PROVINCE, AND THEIR TECTONIC SIGNIFICANCE

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.