辽西凌源地区张家口组的重新厘定及其意义——来自激光ICP-MS锆石U-Pb年龄的制约  

Redefinition of the Zhangjiakou Formation in Lingyuan, western Liaoning and its significance-Constraints from Laser ICP-MS zircon U-Pb ages.

作　　者：张宏[1] 柳小明[1] 高山[1] 张立君[2] 李之彤[2] 杨芳林[2] 王献策[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]中国地质调查局沈阳地质矿产研究所,辽宁沈阳110032 [3]中国地质大学,湖北武汉430074

出　　处：《地质通报》2005年第2期110-117,共8页Geological Bulletin of 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(9501122-3);中国地质调查局项目(200113000052-2)的工作成果

摘　　要：辽西凌源地区张家口组是否存在及其与义县组之间关系的问题一直存在争议。笔者研究表明,凌源地区不仅存在张家口组,而且其与义县组之间为角度不整合接触,它们是不同构造层的产物;义县组的底部层位即为大王杖子层(尖山沟层)。激光ICPMS锆石U-Pb测年得出该地区张家口组火山岩顶界年龄为132.4～130.2Ma,前人得出该地区义县组底部层位(即大王杖子层)的形成时代为126～123Ma,反映该地区张家口组顶部与义县组底界之间存在约6Ma的时间间隔。此时间间隔内研究区不仅发生了构造格架的转换,也是辽西北票—义县地区幔源高镁火山岩的主体喷发期,中国东部中生代岩浆作用也在此时期达到高潮,翼北—辽西地区该时期之后发生了热河生物群大爆发,说明该时期也是一个重要的生物界限。The problems of whether the Zhangjiakou Formation exists in the Lingyuan area, western Liaoning, and its relationships with the Yixian Formation , has long been in dispute. The authors′ study indicates that the Zhangjiakou Formation not only exists but also has an angular unconformity with the Yixian Formation; they are the products in different tectonic horizons. The base of the Yixian Formation is the Dawangzhangzi bed (Jianshangou bed). The laser ICP-MS zircon U-Pb dating gave an age of 132.4-130.2 Ma for the top of the volcanic rocks of the Zhangjiakou Formation in the area, while the formation ages of the base of the Yixian Formation (i.e. Daxinfangzi bed) in the area obtained by the predecessors are about 126 to123 Ma. Thus is inferred that there is a time interval of ～6 Ma between the top of the Zhangjiakou Formation and the base of the Yixian Formation in the area. This time interval not only witnessed a transition of the tectonic framework but also was a period of eruption of the bulk part of high-Mg volcanic rocks in the Yixian-Beipiao, western Liaoning. This paper also discusses the biostratigraphic and tectostratigarphic constraints on the timing of Mesozoic magmatism in eastern China, i.e. constraints by the great explosion of the Rehol fauna in the northern Hebei-western Liaoning area.

关 键 词：张家口组 义县组 U—Pb年龄 辽西凌源 

分 类 号：P534.52[天文地球—古生物学与地层学] P597.3[天文地球—地质学]