A set of rhyolite strata, classified as middle-lower Jurassic series in geological mapping, are exposed in Siziwang Banner that across the border between North China Craton and Inner Mongolia-Daxinganling Orogenic Belt. Petrology, geochemistry, zircon U-Pb geochronology and Hf isotope analysis were performed to investigate the petrogenesis and geodynamic significance of the rhyolite strata. The weighted mean 206Pb/238U ages from the rhyolite and rhyolite porphyry by LA-ICP-MS zircon U-Pb dating are 262±2 Ma to 261±2 Ma, suggesting to the late Middle Permian. The volcanic rocks in Siziwang Banner belong to the high-K calc-alkaline series and shoshonite series, which are characterized by high silicon, alkali, and aluminum, depleted calcium and magnesium. The total amount of rare earth element values is high, and the chondrite normalized REE patterns are enriched in LREE relative to HREE, with moderate to strong negative Eu anomalies, enrichment of large ion lithophile elements Rb, Th and LREE, and depletion of Nb, Ta, Sr and Ba. The volcanic rocks have obviously negative Hf values (-25.97~-11.94), indicating that they may be derived from the partial melting of the ancient crust. The volcanic rocks have high-silica rhyolite characteristics, suggesting that they have undergone significant fractional crystallization and are related to the heating of deep mantle derived magma. The geochemical features and various tectonic discrimination diagrams of the volcanic rocks suggest that the volcanic rocks in Siziwang Banner area were formed in a post-collisional extensional setting.

对华北克拉通与兴蒙造山带结合部位的内蒙古四子王旗地区出露的一套原定为中?下侏罗统的流纹岩进行岩石学、岩石地球化学、锆石U-Pb同位素年代学和Hf同位素组成研究, 确定其岩石成因及地球动力学意义。新获得的流纹岩和流纹斑岩LA-ICP-MS锆石U-Pb 年龄分别为262±2和261±2 Ma, 表明流纹岩的时代应为中二叠世晚期。四子王旗地区流纹岩多属高钾钙碱性系列和钾玄岩系列岩石, 具有高硅、高碱、富铝以及贫钙、贫镁的特征。稀土元素总量较大, 配分曲线明显右倾, 具有中度到重度Eu负异常, 富集大离子亲石元素Rb, Th和轻稀土元素, 亏损Nb, Ta, Sr和Ba等元素。火山岩的ε_Hf(t)为负值(-25.97~-11.94), 可能主要来源于古老地壳熔融岩浆。该套火山岩具有高硅流纹岩的地球化学特征, 表明岩浆经历过结晶分异过程, 岩浆喷出与深部幔源岩浆的加热有关。结合相关构造判别图解, 判断该套火山岩可能形成于后碰撞伸展阶段。