Abstract: 　　
　　Longmu Co-Shuanghu plate suture zone is in the northern part of Qinghai-Tibet Plateau, which is an important window to study the evolution of the Paleo-Tethys Ocean. At present, the geodynamic mechanism of ocean basin closure is not clear. Late Triassic igneous rocks are widely distributed on both sides of the Longmu Co-Shuanghu suture zone, which provides key research materials for studying the tectonic-magmatic process during the closure of the Paleo-Tethys Ocean. In this paper, zircon LA-ICP-MS U-Pb dating and Lu-Hf isotope, as well as whole-rock geochemistry and Sr-Nd isotope analyses were carried out on the granite bodies in the Amugangri area in the eastern part of the suture zone. The zircon dating results are 213~212 Ma, which represents the age of formation of the granite, slightly later than the peak metamorphism age of the high-pressure metamorphic zone in the area. The rocks have high SiO₂ (56.88%~70.35%) and Al₂O₃ (14.45%~16.82%) contents, with variable the K₂O (1.84%~5.47%) and all-alkali contents (K₂O+Na₂O=3.67%~9.51%). The negative P2O5-SiO2 correlation and hornblende indicate an I-type granitoid affinity. The chondrite-normalized rare earth element diagram shows a right-dipping type with obvious Eu-negative anomaly, indicating that there is a certain degree of plagioclase separation or residue in the source area. The trace element partition curves of the samples are basically consistent, with strong enrichment of large ionic lithophilic elements such as K, Th, U, Rb, and La, and strong loss of high-field-strength elements such as Nb, Ta, P, and Ti. In addition, their high I_Sr (0.713530~0.715744) and negative zircon ɛ_Hf (t) values (–19.2~–7.1) and ɛ_Nd (t) values (–11.1~–8.9) characteristics suggest that these granites may have originated from partial melting of ancient crustal materials. The mixed simulation indicates that about 10% ~ 20% mantle-derived basic magma is mixed into the granite source area.Combined with regional geologic data, it is tentatively suggested that the Amugangri body may have formed in a post-collisional environment. Accompanied by the closure of the ocean basin and plate breakoff, lithe upwelling of mantle magma induced strong Late Triassic magmatism in the region, emplaced along the suture zone, which are the petrological evidence for the closure of the Paleo-Tethys Ocean.
　　Longmu Co-Shuanghu plate suture zone is in the northern part of Qinghai-Tibet Plateau, which is an important window to study the evolution of the Paleo-Tethys Ocean. At present, the geodynamic mechanism of ocean basin closure is not clear. Late Triassic igneous rocks are widely distributed on both sides of the Longmu Co-Shuanghu suture zone, which provides key research materials for studying the tectonic-magmatic process during the closure of the Paleo-Tethys Ocean. In this paper, zircon LA-ICP-MS U-Pb dating and Lu-Hf isotope, as well as whole-rock geochemistry and Sr-Nd isotope analyses were carried out on the granite bodies in the Amugangri area in the eastern part of the suture zone. The zircon dating results are 213~212 Ma, which represents the age of formation of the granite, slightly later than the peak metamorphism age of the high-pressure metamorphic zone in the area. The rocks have high SiO₂ (56.88%~70.35%) and Al₂O₃ (14.45%~16.82%) contents, with variable the K₂O (1.84%~5.47%) and all-alkali contents (K₂O+Na₂O=3.67%~9.51%). The negative P2O5-SiO2 correlation and hornblende indicate an I-type granitoid affinity. The chondrite-normalized rare earth element diagram shows a right-dipping type with obvious Eu-negative anomaly, indicating that there is a certain degree of plagioclase separation or residue in the source area. The trace element partition curves of the samples are basically consistent, with strong enrichment of large ionic lithophilic elements such as K, Th, U, Rb, and La, and strong loss of high-field-strength elements such as Nb, Ta, P, and Ti. In addition, their high I_Sr (0.713530~0.715744) and negative zircon ɛ_Hf (t) values (–19.2~–7.1) and ɛ_Nd (t) values (–11.1~–8.9) characteristics suggest that these granites may have originated from partial melting of ancient crustal materials. The mixed simulation indicates that about 10% ~ 20% mantle-derived basic magma is mixed into the granite source area.Combined with regional geologic data, it is tentatively suggested that the Amugangri body may have formed in a post-collisional environment. Accompanied by the closure of the ocean basin and plate breakoff, lithe upwelling of mantle magma induced strong Late Triassic magmatism in the region, emplaced along the suture zone, which are the petrological evidence for the closure of the Paleo-Tethys Ocean.