The Hegenshan suture of the eastern Central Asian Orogenic Belt(CAOB) has developed the Late Paleozoic SSZ??type ophiolites—arc magmatic rocks and Mesozoic volcanic rocks.The spatial??temporal distribution and genetic relationship between Mesozoic volcanic rocks and late Paleozoic ophiolite—arc magmatic rocks have gradually become one of the important scientific issues in the tectonic evolution of the Hegenshan suture.Therefore,this study carried out zircon geochronology,geochemistry, genesis and tectonic environment on the Asagetu Mesozoic volcanic rocks in order to provide new evidence for the tectonic evolution of the Hegenshan suture.Methods: Based on field geological surveying, petrology,geochemistry and LA-ICP-MS zircon U-Pb geochronology of the Asagetu volcanic rocks exposed in the sothern part of the Diyanmiao ophiolitic melange belt of the Hegenshan suture in Xiwuqi of Inner Mongolia,this paper discusses petrogenesis and tectonic environment of the volcanic rocks,and slab breakoff—post orogenic extension of the Paleo-Asian Ocean.Results:The Asagetu volcanic rocks are mainly composed of trachyandesite,trachyte and trachydacite.Zircon LA-ICP-MS U-Pb dating for the trachyandesite volcanic rocks shows that the age of volcanic rocks is 132.1±0.7Ma. Petrogeochemistry shows that volcanic rocks belong to shoshonite series.Rocks with high Na2O+K2O(7.61%~10.35%),K2O(3.94%~6.04%),Al2O3(16.32%~17.99%) and low TiO2(0.45%~0.95%) are obviously enriched in LILEs(Rb,Ba and U) and LREEs,and depleted in HFSEs (Nb,Ta and Ti).The contents of rare earth elements range from 109.62×10-6 to 174.68×10-6.The chondrite normalized REE distribution patterns are of right inclined shape.Combined with the crust—upper mantle electrical structure and the temporal—spatial distribution of the Late Paleozoic ophiolites—arc magmatic rocks and Mesozoic post orogenic A-type granites in the Hegenshan suture,the geodynamic model of the subducted slab break off—post orogenic extension of the shoshonitic volcanic rocks has been preliminarily established.Conclusions:This study determines the Early Cretaceous (132.1±0.7Ma) Asagetu volcanic rocks,which are related to the previous oceanic subduction and formed in the subsequent subducted slab break off—post orogenic extension tectonic setting.The fluids dehydrated from the subducted oceanic crust of the Paleo-Asian Ocean metasomatized the overlying mantle to form the enriched mantle of the Hegenshan suture.The subsequent subducted slab break off—the post orogenic extension triggered partial melting of the enriched mantle to produce the shoshonitic magma.The discovery and confirmation of the Asagetu shoshonitic rocks in the Early Cretaceous provide new evidence for the Paleo-Asian Ocean subducted slab break off—post orogenic extension.Acknowledgements:This study was financially supported by the National Natural Science Foundation of China (grant No.41972061) and the China Geological Survey (grants No.1212011120711 and 1212011120701).