内蒙古北山造山带花岗岩地球化学、锆石U-Pb年龄和Hf同位素特征及地质意义

砾石滩地区位于内蒙古额济纳旗西部，晚古生代花岗岩出露广泛，是研究北山造山带晚古生代地质演化的关键地区.锆石LA-MC-ICP-MS U-Pb测年结果显示，该地区的花岗岩形成于晚石炭世，其中英云闪长岩年龄为310.8±1.4 Ma，花岗闪长岩年龄为310.3±1.4 Ma和306.0±1.2 Ma，二长花岗岩年龄为308.7±1.4 Ma.岩石学及化学成分显示其为准铝质-弱过铝质、中钾钙碱性系列岩石；稀土配分曲线呈现轻稀土元素相对富集的右倾分布特征，弱负铕异常（δEu为0.7~0.9）；岩石富集大离子亲石元素Rb、K等，具有负的Nb、Ta和Ti异常；英云闪长岩、花岗闪长岩具有不均一的ε_Hf（t）值（3.8~14.8）、（7.3~14.0），二阶段Hf同位素模式年龄t_DMC分别为378~1 083 Ma、433~868 Ma.北山造山带北部晚石炭世英云闪长岩、花岗闪长岩、二长花岗岩的形成与壳幔混合有关，产生于大洋岩石圈俯冲过程中，形成于陆缘弧环境，该过程诱发了地幔对流，因而产生了幔源岩浆底侵，并将元古宙基底岩石熔融，壳幔混合之后形成晚石炭世大规模花岗岩类. 

Geochemical Characteristics,Zircon U-Pb Age and Hf Isotope and Geological Significance of Granitoid in Beishan Orogenic Belt

Lishitan area is located in west of Ejin County of Inner Mongolia, where Late Paleozoic granitoid is exposed in a wide range. And it's a key area to the geology evolution research of Beishan orogenic belt in Late Paleozoic. The zircon LA-MC-ICP-MS U-Pb dating results show that the granitoid in this area was formed in the Late Carboniferous, the tonalite was formed at 310.8±1.4 Ma, the granodiorite was formed at 310.3±1.4 Ma, 306.0±1.2 Ma respectively, and the monzonitic granite was formed at 308.7±1.4 Ma. The petrology and lithochemistry demonstrate that the tonalite, granodiorite and monzonitic granite belong to quasi-aluminous to weakly peraluminous rocks and middle-K calc-alcaline series. The tonalite, granodiorite and monzonitic granite are enriched in LREE and part of large iron lithophile elements, including Rb, K et al., relatively depleted in HREE, Nb, Ta and Ti with weakly negative europium anomaly (δEu is 0.7-0.9).The ε_Hf(t) values of tonalite and granodiorite are variable, ranging from 3.8 to 14.8 and 7.3 to 14.0 respectively. And the two stage Hf isotope model ages (t_DMC) range from 378 to 1 083 Ma and from 433 to 868 Ma respectively. The formation of tonalite, granodiorite and monzonitic granite is related with crust-mantle mixing, which were formed in the active epicontinental arc environment in the process of the ocean lithosphere subduction in Northern Beishan orogenic belt in Late Carboniferous. Mantle convection was caused by the process, thus led to mantle-derived magma invasion, which melted the Proterozoic basement rocks, and massive granitoids formed after crust-mantle mixing in Late Carboniferous.