Pb Isotope Mapping in the Tongbai-Dabie Orogenic Belt, Central China

Tongbai-Dabie orogenic belt in Central China is a part of the collisional belt between the Yangtze and North China cratons.It represents one of the most extensive ultrahigh-pressure (UHP)and high-pressure (HP)metamorphic rocks in the world.The Pb isotope mapping in this area is a significant method to constrain the crustal structure and tectonic evolution and to identify the tectonic boundaries within the vertical tectonic stack.Based on the Pb isotope compositions of the Dabie complex (DBC),the Tongbai complex (TBC),UHP and HP metamorphic rocks and associated foliated granites,the lower metamorphosed rocks from North Huaiyang (NHY)tectonic belt,and Cretaceous granites in the Tongbai-Dabie orogenic belt,we determined the Pb isotope geochemical map of the Tongbai-Dabie orogenic belt.The Pb isotope map shows that the Pb isotope compositions are similar within each geological body or lithotectonic unit,but the Pb isotope compositions of different lithotectonic units show systematic variations in the Tongbai-Dabie orogenic belt.The NHY tectonic belt contrasts strongly with the Tongbai-Dabie UHP-HP metamorphic belt in Pb isotope compositions. It is suggested that the line along the Xiaotian-Mozitan fault,the north limit of the Tongbai-Dabie UHP and HP metamorphic rocks,represents an important tectonic boundary.Within the Tongbai-Dabie HP -UHP metamorphic belt,to the south of Xiaotian-Mozitan fault,the vertical variations of Pb isotope compositions in different lithotectonic units and the spatial relationship among different major lithotectonic units have been constrained.