Post-orogeny of the Hegenshan suture zone: Zircon U-Pb age and geochemical constraints from volcanic rocks of the Manketouebo Formation

Based on field geological survey, petrology, geochemistry and LA-ICP-MS zircon U-Pb geochronology of the Baiyinrui volcanic rocks of the Manketouebo Formation exposed in the Meilaotewula SSZ-type ophiolite of the Hegenshan suture zone in Xi Ujimqin Banner of Inner Mongolia, this paper discusses the petrogenesis and tectonic setting of the volcanic rocks and post-orogeny of the Hegenshan suture zone. Petrogeochemical studies show that the volcanic rocks of the Manketouebo Formation in Baiyinrui area are mainly rhyolite with high SiO₂, K₂O and Na₂O+K₂O content, higher Ga/Al ratio and relatively poor CaO, MgO, Sr, Ba, Eu, Ti and P content. The REE content is relatively low. The REE distribution curve exhibits weak right-inclined gull-wing distribution. Petrological and geochemical characteristics show that the rhyolite of the Manketouebo Formation in this area is of Atype rhyolite origin, formed in post-orogenic extensional tectonic setting, and is a product of post-orogenic A-type magmatism, reflecting post-orogenic extensional process. The results of LA-ICP-MS zircon U-Pb isotope dating show that the rhyolite was formed at 158.0±0.7Ma, indicating that the rhyolite of the Manketouebo Formation erupted in the Late Jurassic, reflecting the Late Jurassic post-orogenic A-type magmatism event in the Hegenshan suture zone. Combined with the study of the time and space evolution of the Carboniferous ophiolites, Carboniferous-Permian island arc magmatic rocks and Middle Triassic-Early Cretaceous post-orogenic A-type magmatic rocks in the Erenhot-Hegenshan suture zone, it is considered that the Erenhot-Hegenshan suture zone underwent the evolution stage and dynamic process of post-orogenic extension during the Middle Triassic-Early Cretaceous after the final suture stretching in the Late Permian-Early Triassic.