早古元古代花岗质片麻岩类在华北克拉通孔兹岩带乌拉山地区广泛出露,是记录该区陆壳增生及构造演化的主要物质载体.4件代表性花岗质片麻岩样品的LA-ICP-MS锆石U-Pb年代学分析表明,它们形成于～2.45Ga,并经历了～2.45 Ga及约1.89～1.95Ga多期变质热事件；它们的岩石地球化学分析结果显示,稀土元素含量较高(∑REE =301×10-6 ～909×10-6),富集轻稀土元素、亏损重稀土元素,(La/Yb)N比值在13 ～56之间,无明显Eu异常(Eu/Eu*=0.76 ～1.81,平均为1.18),具有较高的Sr含量(在495×10-6 ～ 895×10-6之间),低的Yb含量(在0.5 ×10-6 ～2.61×10-6之间)；微量元素原始地幔标准化蛛网模式图显示,强烈亏损Nb,Ta,Th,U及Ti等高场强元素,富集Ba,K,Rb及Sr等大离子亲石元素；它们为镁质、准铝质至弱过铝质、高钾钙-碱性系列,指示其可能形成于活动大陆边缘岛弧环境玄武质下地壳的部分熔融.暗示该区早古元古代时期的弧陆增生作用,并经历了从弧陆增生、陆-陆碰撞造山到造山后伸展的构造演化历史.%Early Paleoproterozoic granitoid gneisses are widely distributed in Ulashan area in the khondalite belt, North China Craton, they record continent-crustal growth and tectonic evolution in the study area. The LA-ICP-MS U-Pb analyses of zircons from four representative granitoid gneiss samples collected from the study area unraveled that they formed at ～ 2. 45Ga, and experienced polyphase metamorphic events at ～ 2. 45Ga and 1. 89 ～ 1. 95Ga. The geochemical analyses of the Early Paleoproterozoic granitoid gneisses show they are characterized by high REEs contents ( ∑ REE = 301 × 10-6 ～ 909 × 10-6) , enrichment in light REE and depletion in heavy REE with (La/Yb) N ratios of 13 ～ 56. They have weakly positive and/or negative Eu anomalies (Eu/Eu * = 0. 76 ～ 1.81,average 1. 18) , high Sr content (495 ×10-6 ～895 ×10-6) and low Yb content (0. 5 × 10-6 ～2. 61 × 10-6). Their primitive mantle normalized trace element spider diagrams show they are strongly depleted in high field-strength element Nb, Ta, Th, U, and Ti, and are enrich in large ion lithophile element Ba, K, Rb and Sr. They are magnesian, high-K calc-alkalic and metalumous-weakly peraluminous, indicating that they originated from partial melting of basaltic lower crust under island arc on margin of active continent. It is suggested that there existed arc-continent accretionary process during Early Paleoproterozoic, and experienced tectonic evolutional history of arc-continent accretion, continent-continent collision and extensions post-orogen in Ulashan area.
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