Sm Nd AGES AND GEOLOGICAL SIGNIFICANCE OF AMPHIBOLITES OF THE WUGUAN GROUP COMPLEX ON THE SOUTHERN SIDE OF THE SHANGDAN FAULT ZONE IN THE EAST QINLING MOUNTAINS

The “Wuguan Group Complex" is a metamorphosed sedimentary volcanic series disintegrated from the north part of the original Devonian Liuling Group.The amphibolites （metabasic volcanic rocks） in this tectono lithostratigraphic unit have been determined to have a Sm Nd isochron age of（1382±30） Ma with I Nd =0.511186±1（2σ） and ε Nd （T）=+6.51, indicating that the bulk of the metamorphic series of the “Wuguan Group Complex" was formed in the Middle Proterozoic.This result reflects the process of tectonic development and evolution of the Qinling orogenic belt in the Middle Proterozoic.