Age and petrogenesis of the Anletun pluton in Ar Horqin Banner, Inner Mongolia and its implications for the major suture zone of the Paleo-Asian Ocean

This paper reports petrology, zircon U-Pb dating, and element and isotope geochemical analyzing results for the Anletun pluton in Ar Horqin Banner, Inner Mongolia with the aim of revealing the formation age and petrogenesis of this pluton, and discussing its tectonic significance.Zircon LA-ICP-MS U-Pb dating results indicate that the Anletun pluton formed at 275 ±1 Ma, i.e., the Early Permian, not the early Jurassic as previously believed.Lithological and geochemical analysis show that the Anletun pluton are composed mainly of a suite of quartz monzodiorites, granodiorites, and monzogranites.They have high Na₂O and low K₂O contents, belong to the middle-K calc-alkaline and metaluminous series, display positive Eu anomalies, and are enriched in large ion lithophile elements(LILEs)such as Rb, Ba and K, and depleted in high field strength elements(HFSEs)such as Nb, Ta and Ti.Geochemical compositions of the pluton are similar to those of Ⅰ-type granites formed in a subduction zone at active continental margin.The zircon ε_Hf(t)values of the sample range from -7.0 to -1.9.Together with the crustal nature of enrichment in Nb, Ta, and depletion in Th, the Anletun pluton probably originated by partial melting of ancient lower crustal material.By contrast to the regional geology between the north margin of the Sino-Korean paleo-plate and the south accretionary margin of the Siberian paleo-plate, it is speculated that the Anletun pluton formed in an active continental margin setting related to the southwards subduction of the Paleo-Asian oceanic plate beneath the Sino-Korean paleo-plate, and was attached to north accretionary zone of the Sino-Korean paleo-plate in the Paleozoic.