Zircon U-Pb Ages of Paleoproterozoic Metabasites from the Tongbai Orogen and Their Geological Significance
桐柏造山带古元古代变质基性岩的锆石U-Pb年龄及其地质意义

The Tongbai orogen is situated at the junction between the Qinling and Dabie orogenic belts.Its northern part corresponds to the North Qinling medium-to high-grade metamorphic complexes,whereas the southern part belongs to the westward continuation of the Dabie HP/UHP metamorphic complexes.Zircon U-Pb dating reveals a protolith age of(1961±23) Ma and a zircon recrystallization or growth age of(1949±51) Ma for an eclogite,and a metamorphic age of(1936±26) Ma for a garnet amphibolite(retrograded eclogite?).These data suggest that these rocks might have suffered Paleoproterozoic metamorphism prior to Permian-Triassic HP metamorphism.Based on the available geochronological data from the Tongbai-Dabie-Sulu orogen,the authors have inferred the existence of two episodes of Paleoproterozoic tectonothermal events in northern Yangtze block.The first episode occurred at 1.97-1.93 Ga,probably related to the assembly of the Columbia supercontinent.The second episode took place at 1.85-1.82 Ga,resulting either from the protracted assembly of the Columbia supercontinent or from the accretionary orogenesis along the northern margin of the Yangtze block.