LA-ICP-MS zircon U-Pb dating of Paleoproterozoic pluton in northern Altun area and its geological implications

North Altun region is one of the main regions where the metamorphic basement of the Tarim craton is exposed.In this pa-per, LA-ICP-MS U-Pb dating was conducted on zircon grains from syenogranite and granitic gneiss that have intrusive contact rela-tionship with each other.Most zircons from the syenogranite are characterized by oval shape, typical oscillatory zoning, and residual cores in some grains.The higher Th/U ratios, depletion of LREE and enrichment of HREE, an obvious negative Eu anomaly, and positive Ce anomaly indicate that they are of magmatic origin.The dating results yielded two age groups of weighted mean ages of 1903±13 Ma and 2506±55 Ma.The former age represents the crystallization age of the intrusions, and the latter one represents the age of inherited zircon.Combined with available regional chronologic data, the authors hold that ancient basement zircons of Archean Milan Group may have been involved in the process of granite magma intrusion.Most analyzed spots are clustered around 1802±28 Ma, which represent the crystallization age of the granitic gneiss.The other five analyzed spots yielded ²⁰⁷Pb/²⁰⁶Pb ages of 1911~1951 Ma, implying that part of the granite material was captured in the process of magmatic emplacement.The existing regional geo-logical and isotopic chronologic data suggest that northern Altun region may exist 2.0~1.8 Ga tectonic thermal events.So the crystalli-zation age of granitic rocks 1.9~1.8 Ga directly confirms the existence of the magmatism at 1.9 Ga, such a tectonic magmatic event is consistent with the global collisional orogeny events related to the evolution of Columbia supercontinent, and this can provide new evidence for the exploration of Precambrian tectonic thermal event and its evolution history along the Altun tectonic belt.The forma-tion of granitic gneiss in Late Paleoproterozoic at 1802±28 Ma may represent the post-orogenic stage in North Altun region.