U–Pb and 40Ar/39Ar geochronology of the Tongbai complex, central China: Implications for Cretaceous exhumation and lateral extrusion of the Tongbai–Dabie HP/UHP terrane

The Tongbai orogen in the middle of the Qinling–Tongbai–Dabie–Sulu orogenic belt is one of the most important portions for understanding the tectonic framework and evolution between the Sino-Korean and Yangtze cratons. In this paper, we report new U–Pb and 40Ar/39Ar age data from the Tongbai complex in order to constrain the extensional processes and late exhumation of HP/UHP terranes. Zircon U–Pb dating of different rock types in the Tongbai complex reveals the intrusion of voluminous granitic magmas at 139 ± 2 Ma, contact metamorphism and migmatization of the Triassic metamorphic enclaves at 136 ± 2 Ma, and syn-deformational emplacement of pegmatite veins at 131 ± 1 Ma. 40Ar/39Ar thermochronology on hornblende, muscovite and biotite coupled with available structural data indicates two episodes of deformation (cooling) at ca.135–120 Ma and ca. 100–90 Ma. The predominant ductile shearing structures, including regional subhorizontal NWW-SEE stretching lineations in the whole Tongbai complex and sinistral and dextral shear senses along its northern and southern boundaries, were formed during the first deformational episode. Regionally, the Cretaceous magmatism, metamorphism, migmatization, deformation and cooling processes in the Tongbai complex are comparable with those in the Dabie–Sulu region, suggesting the evolution of the Tongbai–Dabie–Sulu orogen within the same extensional tectonic regime during this time. The Cretaceous extensional event is thought to have resulted in the lateral eastward extrusion of the Tongbai–Dabie terrene and exhumation and final exposure of the HP/UHP rocks from mid-upper crustal depths.

► Gneissic granites dominating the Tongbai complex were emplaced at ca. 140 Ma.
► The Tongbai complex underwent two episodes of deformation (cooling) at ca. 140–120 Ma and ca. 100–90 Ma.
► Cretaceous is crucial for the final exhumation of HP/UHP rocks in Tongbai orogen.