The Early Cretaceous tectonic evolution of the southern Great Xing'an Range, northeastern China; new constraints from A2-type granite and monzodiorite

The widespread Early Cretaceous plutons intruding along the southern Great Xing'an Range (SGXR) provide evidence for tectonic evolution of the region. Petrological, geochemical, zircon U-Pb geochronology, and zircon Hf isotopic studies are conducted on intrusions from Bianjiadayuan and Hongling areas. These suites classify as A2-type granites and monzodiorites, respectively. The 138-133 Ma A2-type granites originated from partial melting of continental crustal materials at high temperatures and shallow depths with significant addition of juvenile mafic lower crust sourced from a metasomatized mantle. The 136-134 Ma monzodiorites originated from the partial melting of an enriched mantle that was modified by melts of a previously subducted slab coupled with crustal contamination. The Early Cretaceous magmatism in the SGXR occurred in two periods: approximately 145-136 Ma (peak at approximately 139 Ma; epsilon Hf (t) = 5 to 10) and approximately 136-130 Ma (peak at approximately 131 Ma; epsilon Hf (t) = -10 to 15). The Early Cretaceous granite-monzodiorite suite in the SGXR suggests a bimodal magmatism in an extensional setting. The approximately 145-130 Ma magmatism may have been triggered by asthenospheric upwelling induced by the Mongol-Okhotsk oceanic slab breakoff and large-scale lithospheric delamination resulting from post-orogenic extension. The variation of subduction direction of the Paleo-Pacific Ocean likely triggered a change in stress regime at ca. 136 Ma and likely promoted the lithospheric delamination beneath the SGXR resulting in intense magmatism originating from various sources. As such, the Paleo-Pacific Oceanic subduction likely played an important role in the Early Cretaceous magmatism in the SGXR.