中文摘要：

在秦皇岛市柳江地区出露最古老的沉积岩为青白口系长龙山组石英砂岩，该石英砂岩与下伏的新太古代钾质花岗岩呈不整合接触。LA-ICPMS锆石U-Pb测年显示该区长龙山组石英砂岩中碎屑锆石年龄分布在2635～2487Ma之间，其物质源区较单一。与北京-蓟县标准剖面相比，本研究区在较长的一段地质时期为古陆壳的剥蚀区，直至新元古代早期，又沉积了长龙山组滨海相碎屑岩。碎屑锆石Hf同位素组成显示，它们的源区物质虽然有不同程度的壳幔混合，但主要来自于古老的地壳物质再循环，暗示在-2．5Ga其碎屑物质源区的地壳已经达到一定的规模和厚度。

英文摘要：

With the development of the in situ zircon SHRIMP U-Pb dating method and laser ablation ICP-MS, the study of the age distribution of detrital zircons from sedimentary rocks has become an effective way to find the source area of clastic material and also become an important topic all over the world. However, during zircon laser ablation （LA）-ICPMS dating, the U-Pb isotopic fractionation remains one of the principal obstacles for precise zircon dating. The experiments performed by the authors demonstrate that a low laser frequency （5 Hz or 6 Hz） would reduce element fractionation during laser ablation. The U-Pb ages of international zircon standards GJ-1 and the laboratory zircon standard SK10-2 were measured by LA-ICP-MS in 20μm spot size at 5 Hz laser frequency. The reduce mean 2~6pb/238U ages obtained in our analysis are in good agreement with the published values. Quartz sandstone from Changlongshan Formation of Qingbaikou System, the oldest metasedimentary rock in Liujiang area of Qinhuangdao City, was deposited unconformably on the Neoarchean potassic granite. Detrital zircons from the quartz sandstone have 207Pb/206pb ages of 2 635 Ma to 2 487 Ma. A comparison with the Beiijng-Jixian stratatigrphie section, from Early Proterozoic, the study area experienced a long period of weathering and erosion, and then began to deposit on the surface and become the source area of elastic sedimentsof the Changlongshan Formation until the early Neoproterozoic. HI tsotoplc compositions of the detrital zircons indicate that the clasts were main-ly derived from the reworked ancient crust, suggesting that the mass of the continental crust was largely established at --2.5 Ga in its source area.