关键词: 北山造山带, 黄草滩岩体, 锆石UPb定年, 大洋俯冲, 活动陆缘

Abstract: The Beishan orogenic belt is the transition zone located between the east and west part of southern margin of the Central Asian Orogenic Belt.It is the key area for the study of contact relationship between west and east of the Central Asian Orogenic Belt. The magma information during the orogenetic process was recorded in the granites, as a typical represent of the Huangcaotan pluton in the southern of Beishan, which consists mainly of diorite and granodiorite. Zircon UPb dating yields the crystallization ages of （402±3 )Ma for diorite and （394±7) Ma for granodiorite, respectively. The Huangcaotan pluton displays typical geochemical characteristics of Itype granite: high SiO2 contents （5924%-7154%), high Na2O contents （376%-409%), and aluminumweakly peraluminous affinity（A/CNK=094-111). The relatively lower level of ∑REE, enriched LREE, obvious fractionation of heavy and light rare earth, slightly negative Eu anomaly, together with the highly enriched Rb, Th, U and K in LILE and depleted Nb, P, Hf and Ti in HFSE, indicate subductionrelated geochemical features. The granite may be derived from partial melting of metabasaltic rocks in the middlelower crust caused by underplating of mantlederived magma and contaminated by the mantlederived material. Together with regional geology, it is proposed that the Huangcaotan pluton was formed in volcanic arc on an active continental margin and may be the product of magmation related to the northward subduction of PaleoAsian Ocean in Liuyuan area, representing an important magmatism related to oceanic slab subduction from the Early Devonian in the southern of Beishan orogenic belt.

Key words: Beishan orogenic belt, Huangcaotan pluton, zircon UPb dating, oceanic subduction, active continental margin