辽西凌源地区义县组下部层位的U-Pb测年及意义  

U-Pb Isotopic Age of the Lower Yixian Formation in Lingyuan of Western Liaoning and Its Significance

作　　者：张宏[1] 柳小明[1] 袁洪林[1] 胡兆初[1] 第五春荣[1] 

机构地区：[1]西北大学地质学系大陆动力学重点实验室,西安710069

出　　处：《地质论评》2006年第1期63-71,共9页Geological Review

基　　金：长江学者和创新团队发展计划资助项目的成果

摘　　要：辽西凌源地区义县组的下部层位为大王杖子层，通过对该层位及相关层位样品中锆石的LA—ICP—MS的U—Pb测年，获得大王杖子层的形成年代为125～122Ma。经过综合分析，得出以下初步结论：①辽西凌源地区与北票-义县地区的义县组底界是不等时的；凌源地区义县组下部层位在时代上相当于北票-义县地区的义县组尖山沟层（砖城子层）；②凌源地区的张家口组与义县组之间有约5～6Ma的时间间隔。这不仅验证了凌源地区张家口组与义县组之间为角度不整合接触的可靠性，也暗示该5～6Ma的间隔期为冀北-辽西地区中生代构造格架转换的关键时期；该时期也是我国东北地区中生代岩浆作用的鼎盛时期；同时在冀北-辽西地区，该间隔期之后发生了热河动物群的大爆发，说明该间隔期也是一个重要的生物界限。A new LA-ICP-MS zircon U-Pb dating gave an age of 125-122 Ma for the Dawangzhangzi bed in the lower Yixian Formation. Together with previous studies, the writers draw conclusions as follows： （1） the bottom of the Yixian Formation in the Lingyuan and Beipiao-Yixian regions is not synchronous. The Dawangzhangzi bed in Lingyuan corresponds to the Jianshangou （Zhuanchengzi） bed in the Beipiao-Yixian region in age. （2） The Yixian Formation is in angular unconformity with the Zhangjiakou Formation in the Lingyuan area. The isotopic result suggests that the Yixian Formation have a 5-6 Ma interval with the Zhangjiakou Formation, which not only proved that the angular unconformity of the two formations is credible, but also reflect that the 5 - 6 Ma interval is the key period of the transition of tectonic framework in the Mesozoic in northern Hebei-western Liaoning area. In the interval, magmatism was in the peak stage in northeastern China. Moreover, after the interval, the Jehol Fauna prospered, suggesting that the interval is an important biological interface in the northern Hebei-western Liaoning area.

关 键 词：U—Pb同位素测年 LA—ICP—MS 义县组 辽西凌源 

分 类 号：P597.3[天文地球—地球化学]