中文摘要：

1∶20万地质图和早期的研究认为胶北西北部的屺坶岛出露的是震旦纪或早古生代的蓬莱群。本文对此处地层中的石英粉砂岩和位于其下的火山凝灰岩开展了SHRIMP锆石U-Pb定年工作。火山凝灰岩中12个点的U-Pb分析给出了124.2±2.3Ma的结晶年龄,表明出露在屺坶岛的这套地层属于下白垩统,而不是地质图上标注的震旦系。石英粉砂岩的碎屑锆石分析进一步验证了其沉积时代为早白垩世：通过对石英粉砂岩50个点的分析,获得了430Ma、1.1Ga、1.6Ga、1.8Ga和2.45Ga共5个峰值,其中430Ma的峰值由两个岩浆锆石给出,可能来源于鲁西下常庄三叠纪磁铁角闪岩岩体中的继承锆石。石英粉砂岩的碎屑锆石的其他峰值年龄和长岛石英岩的碎屑锆石的峰值吻合,暗示其碎屑主要来源于周边蓬莱群。此外,屺坶岛的石英砂岩和胶莱盆地下白垩统莱阳群的碎屑锆石年龄图谱明显不同,暗示它们来源于不同的源区。结合区域正断层活动历史,推测在胶北地区屺坶岛可能存在一个早白垩世伸展盆地,与胶莱盆地之间由玲珑和郭家岭岩体构成的隆起分隔。

英文摘要：

It is traditionally believed that the bedrocks exposed at the Qimudao of the Jiaobei region belong to the Penglai Group of Sinian and Early Paleozoic. However, the newly acquired SHRIMP zircon U-Pb a- ges from the siltstone and volcanic tuff of the mapping unit of ＂Penglai Group＂ tells a different story. 12 analyses of zircon grains from the tuff yielded a crystallization age of 124.2 ± 2.3 Ma, indicating that the rock succession at the Qimudao was deposited during Early Cretaceous, rather than Sinian. Detrital zircon U-Pb age data of fifty zircon grains, moreover, from the siltstone can be grouped into five age populations： 430 Ma, 1.1 Ga, 1.6 Ga, 1.8 Ga and 2.45 Ga. The 430 Ma peak comes from two magmatic zircons with oscillatory zonation, and could be sourced from the eroded Triassic Xiachangzhuang magnetite amphibolite in the Luxi region. Other age peaks from the siltstone are rather consistent with the detrital zircon peaks of the quartzite of the Penglai Group found in the nearby Changdao, suggesting a possible recyclic origin. In addition, these peak populations are conspicuously different from the detrital zircon U-Pb populations of the coeval Laiyang Group in the Jiaolai Basin to the south of the study area, implying proximal and varying source regions for discrete Cretaceous basins in the region. Together with normal faulting activities, it is inferred that there was an Early Cretaceous extensional basin developed in the region.