华北串岭沟组凝灰岩锆石SHRIMP年龄及其地层学意义

Zircon SHRIMP U-Pb age of the Chuanlinggou Formation of the Changcheng Group,North China and the stratigraphic implications

华北克拉通燕辽地区是中国中新元古代沉积地层的标准剖面区。蓟县群和青白口群已经取得了很多重要的高精度定年数据,但是长城群除了顶部大红峪组有了高精度定年以外,其他组还缺乏可靠的高精度定年数据。为了准确标定华北克拉通中元古界长城群串岭沟组的年龄,对采自河北宽城地区神仙岭剖面串岭沟组顶部火山岩凝灰岩锆石进行了SHRIMP U-Pb定年。结果表明所测锆石207Pb/206Pb表面年龄加权平均值为(1 634.8±6.9)Ma(95%置信度,MSWD=1.2,n=23)。可见长城群串岭沟组顶部的准确年龄为(1 634.8±6.9)Ma,表明长城群串岭沟组到大红峪组整体上属于中元古代地层。

The Yanliao area in the North China Craton(NCC)represents a standard section of MesoNeoproterozoic sedimentary strata of NCC.The Jixian and Qingbaikou Groups have gained a substantial amount of important high accuracy dating data.However,reliable high accuracy dating data are still lacking for the Changcheng Group,except for the Dahongyu Formation at the top of the group.Here,in order to accurately determine the geological age of the Mesoproterozoic Chuanlinggou Formation of the Changcheng Group,we collected samples of volcanic tuff rocks from the upper part of the Chuanlinggou Formation in the Shenxianling Section,Kuancheng County,Hebei Province and performed zircon SHRIMP U-Pb dating at the Beijing SHRIMP Center.The zircon dating yielded a weighted mean 207Pb/206Pb age of 1634.8±6.9 Ma(95%confidence,MSWD=1.2,n=23),which,we conclude,is the age of the upper part of the Chuanlinggou Formation.It is suggested,therefore,that the Changcheng Group,from the Chuanlinggou Formation to Dahongyu Formation as a whole,belongs to Mesoproterozoic strata.