中文摘要：

报道了新近在华北北缘西段狼山地区发现的枕状玄武岩的初步定年工作。前人将其时代定为早古生代。对选自玄武岩的32颗锆石进行了LA-ICP—MSU—Pb定年结果表明，玄武岩的锆石大量为捕获基底的锆石。其年龄和锆石内部结构复杂多样。根据锆石内部特征将其划分为4类，其中的板状锆石被定为玄武岩的自生锆石，年龄为晚古生代末期-早三叠世早期。其余均为来自阿拉善地块基底的锆石，主要为古元古代-新太古代和古生代锆石。狼山晚古生代末期的玄武岩可能产自古亚洲洋封闭后由于岩石圈拆沉导致的伸展环境，该期伸展贯穿华北北缘直至阿拉善地块，暗示华北板块与阿拉善地块至少在晚古生代之前就已经拼合在一起了。

英文摘要：

Recent found pillow lava basalts in the southwestern Langshan and its preliminary dating has been reported here. Previous survey had assigned its age at the Early Paleozoic. 32 zircons from pillow lava basalts have been dated using LA-ICP-MS. Most zircons from basalts are captured from the basement, the distribution of ages and internal structures of which are complicated. Four groups of zircons have been distinguished by their internal structures. Among them the tabular zircons have been believed as the autogenetic zir- cons of pillow lava basalts, the ages of these zircons range from the end of Permian to the Early Triassic. The rest zircons in the samples are all from the Alashan basement, among which Paleoproterozoic and Newarchaeozoic zircons and Paleozoic zircons are most. The latest Late Permian Langshan basalts may developed in the extensional tectonics resulting from the delamination of the lithosphere after the closure of the Paleoasian Ocean, the extension of this period occurred along the whole north margin of the North China Plate including the Alashan block, which means that the Alashan block jointed with the North China Plate at least before the Late Paleozoic.