Lying along the eastern Hegenshan suture zone in Horqin Right Middle Banner of Inner Mongolia, the Jurihe A2- type monzogranite intruded into Early Carboniferous Duerji tectonic melange belt. Based on systematic field geological characteristics, petrology, geochemistry, zircon U- Pb chronology of it, the purpose of study is to determine genetic type of pluton, tectonic setting, and provide evidence for the closure time of Hegenshan Ocean, a branch of the Paleo- Asian Ocean. The Jurihe monzogranite is mainly composed of fine- grained and medium- grained monzogranite. LA- ICP- MS zircon U- Pb dating shows that the age of granite is 203.7±1.6 Ma, indicating that formation age is Late Triassic. The granite is geochemically characterized by high SiO2 (71.08%~76.62%) and alkali (Na2O+K2O=7.99%~9.28%), but low CaO (0.25%~1.67%) and MgO (0.05%~0.63%). The obvious negative Eu anomaly (Eu=0.14~0.50), relative enrichment of Rb, Th, U, K and Ga, depletion of Ba, Sr, P and Ti, as well as high 10000Ga/Al (3.62~4.90), TFeO/MgO (3.40~14.80), (Na2O+K2O)/CaO (5.03~31.96) values show characteristics of A2type granite, representing that it was formed in post- orogenic extensional environment. At the same time, combining with the temperature and pressure conditions of magma origin, it is believed that the pluton may be caused by partial melting of crustal hornblende rocks containing plagioclase under the condition of dehydration and subsequent crystallization differentiation in post- orogenic stage. Combined with the spatio—temporal evolution of Early Carboniferous—Late Triassic ophiolites, intra oceanic arcs and post- collisional granitoids in the eastern part of Central Asia Orogenic Belt, suggesting that the Hegenshan Ocean was probably closed at the end- Permian and entered post- orogenic extension stage in Triassic.Methods：Based on field geological surveying, petrology, geochemistry and LA- ICP- MS zircon U- Pb geochronology of the Jurihe monzogranite, this paper discusses the petrogenesis and tectonic setting of the monzogranite, and the final closure time and subduction process of the Hegenshan Ocean.Results：(1) The Jurihe monzogranite was intruded into the Early Carboniferous Duerji tectonic melange belt in the Horqin Right Middle Banner. The LA- ICP- MS zircon U- Pb age is 203.7±1.6 Ma, indicating that its emplacement occurred during the Late Triassic.(2) The Jurihe monzogranite is characterized by high SiO2, rich alkali, and poor CaO and MgO, with A/CNK=0.93~1.14 and A/NK=1.09~1.26. The negative Eu anomaly is significant, and Rb, Th, U, K, and Ga elements are relatively enriched, while Ba, Sr, P, and Ti elements are relatively depleted. Additionally, the 10000Ga/Al, TFeO/MgO, (Na2O+K2O)/CaO values are high, indicating a weakly peraluminous A2- type granite.(3) The Jurihe monzogranite is the product of extension after closure of the eastern Hegenshan suture zone, which provides petrological evidence for the Hegenshan Ocean closing at end- Permian and entering post- orogenic extension stage in Triassic. Partial melting and subsequent crystallization differentiation of shallow crustal materials under low- pressure and high- temperature may be its genesis, which records information on the evolution of post- orogenic plate break- off and mantle derived basaltic magma underplating in the eastern Hegenshan suture zone during Late Triassic.Conclusions:This study determines the Late Triassic (203.7±1.6 Ma) Jurihe monzogranite, which was probably formed in post- orogenic extension setting and is the A2- type granite. The Jurihe A2- type monzogranite might have been derived from underplating of mantle derived basaltic magma caused by the separation of previously subducted plate fragments in the shallow low- pressure environment and subsequent crystallization differentiation. The discovery and confirmation of the Jurihe 2- type monzogranite in the Late Triassic provide new evidence for Hegenshan Ocean closure and subsequent post- orogenic extension setting.