辽西北票—义县地区义县组顶部层位的年龄及其意义  

The age of the top of the Yixian Formation in the Beipiao-Yixian area,western Liaoning,and its importance

作　　者：张宏[1] 柳小明[1] 陈文[2] 李之彤[3] 杨芳林[3] 

机构地区：[1]西北大学地质学系大陆动力学重点实验室,陕西西安710069 [2]中国地质科学院地质研究所同位素开放实验室,北京100037 [3]国土资源部沈阳地质研究所,辽宁沈阳110032

出　　处：《中国地质》2005年第4期596-603,共8页Geology in China

基　　金：科技部2000年度科技基础性工作第35专项;国土资源部专项(2000010403);中国地质调查局地质大调查项目(200113000052-2;200413000024)资助

摘　　要：辽西义县组顶部层位为义县组金刚山层之上的黄花山角砾岩层或流纹岩(二者为同时异相)。通过对该流纹岩样品中锆石的LA-ICP-MS的U-Pb测年,获得其加权平均年龄为(118.9±1.4)Ma～(119.8±1.9)Ma。通过Ar-Ar方法测年,测得了黄花山角砾岩层的下部岩石中灌入的英安斑岩的年龄,其坪年龄为(122.1±0.3)Ma,等时线年龄为(121.8±1.4)Ma。反映义县组顶部层位的形成时期应在122～119Ma。义县组顶部层位年龄的确定,不仅确定了义县组中热河动物群顶部层位(金刚山层)的上限年龄(约122Ma),同时也确定了义县组火山岩形成的上限年龄(118.9±1.4)Ma～(119.8±1.9)Ma。该地区义县组顶部层位的年龄,也是辽西乃至中国东北地区白垩纪大规模岩浆活动结束的年龄。The top of the Yixian Formation in the Beipiao-Yixian area, western Liaoning,the Huanghuashan breccia or rhyolite above the Jingangshan bed of the Yixian Formation. Zircon LA-ICP-MS U-Pb dating of the rhyolite sample gives weighted mean ages of 118.9±1.4-119.8±1.9Ma. In addition, dacite porphyry injected into the lower part of the Huanghuashan breccia is dated by using the ^40Ar/^39Ar method, which has a plateau age of 122.1±0.3Ma and an isochrone age of 121.8±1.4Ma. These age data suggest that the top of the Yixian Formation in the Beipiao-Yixian area formed at 122-119 Ma. The determination of the age of the top of the Yixian Formation defines not only the upper age limit （-122 Ma） for the Rehe fauna-bearing top part of the Yixian Formation （i.e. the Jingangshan bed） but also the upper age limit （-118.9±1.4Ma-119.8＋1.9 Ma） of volcanic rocks of the Yixian Formation. The age of the top of the Yixian Formation in the area is also a very important ending age of large-scale Cretaceous magmatism in western Liaoning and even Northeast China.

关 键 词：LA-ICP-MS 年龄 义县组顶部 辽西 

分 类 号：P588.212[天文地球—岩石学] P597.3[天文地球—地质学]