Abstract: The Permian granitoids are widespread in Urad Zhongqi, Inner Mongolia, and are located on the middle segment of the northern margin of the North China Plate. The granitoids consist mainly of quartz diorite and granodiorite. They show a calc-alkaline I-type affinity and are characterized by dominant biotite in dark mineral, low A/ CNK (0. 77- 1. 04) . They have the geochemical characteristics similar to adakites by ≥56% SiO₂ ( 55. 70% -68. 65% ) , ≥15% Al₂O₃ ( 15. 32% -22. 87% ) , low Y ( 2. 82-20. 89 μg/ g) and Yb ( 0. 25-2. 24 μg/g) , enrichment of LILE ( large-ion lithophile elements) and LREE (e.g. Ba = 627-2124 μg/ g, Sr = 327-968 μg/ g, Sr/Y = 32. 2-211, ( La/Yb)_N = 5. 83-81. 1) , and mostly evidently positive Eu anomalies (δEu = 0. 63-2.25 ). They are interpreted as post-collisional calc-alkaline granitoids, formed mainly by partial melting of the overthickened continental lower crust due to underplating of EM1-type mantle-derived basaltic magma. Biotite ⁴⁰Ar/³⁹Ar ages of Beiqigetao Pluton, Talabuji Pluton, Ageru Pluton and Baoerhantumiao Pluton are respectively 260 ±3, 258 ±1, 260 ±3 and 258 ±2 Ma, which indicate they were emplaced during the Late Permian.

Key words: North China plate, Inner Mongolia, post-collision, adakite, underplating

摘要： 内蒙古乌拉特中旗的华北板块北缘中段发育了大量的花岗岩类, 主要由石英闪长岩和花岗闪长岩组成。岩石具有钙碱性 I 型花岗岩类特征:暗色矿物以黑云母为主, A/ CNK 为 0. 77 ～1. 04 。多数岩体地球化学特征类似于埃达克岩: SiO₂含量为 55. 70% ～68. 65% , Al₂O₃ 含量为 15. 32% ～22. 87% , Y 和 Yb 含量分别为 2. 82 ～20. 89 μg/ g和 0. 25 ～2. 24 μg/ g; 大离子亲石元素( LILE) 和轻稀土元素( LREE) 富集, 如 Ba 含量为 627 ～2124 μg/ g, Sr 含量为 327 ～968 μg/ g, Sr/ Y 为32. 2 ～211, ( La/ Yb)_N为5. 83 ～81. 1; Eu 多为正异常(δEu = 0. 63 ～2. 25)。它们形成于后碰撞抬升的背景, 主要由增厚的下地壳部分熔融形成, 可能与来 自EM1 型富集地幔的玄武质岩浆底侵作用有关。北七哥陶岩体、塔拉布基岩体、阿格如岩体和保尔汗图庙岩体中黑云母的 ⁴⁰Ar/³⁹Ar年龄分别为 260 ±3, 258±1, 260 ±3 和258 ±2 Ma, 表明它们的侵位时代均为晚二叠世。

关键词: 华北板块, 内蒙古, 后碰撞, 埃达克岩, 底侵作用