华北青白口系下马岭组凝灰岩锆石SHRIMP U-Pb定年

Zircon SHRIMP U-Pb dating of the tuff bed in the Xiamaling Formation of the Qingbaikouan System in North China

华北中、新元古代地层一直是建立中国晚前寒武纪地层标准剖面的主要目标,其年代地层位置一直是地学界关注的基础地质问题。然而,许多关键层位仍缺乏高质量同位素年龄的约束。首次在华北青白口系下马岭组凝灰岩中获得大量岩浆型锆石,利用SHRIMPII技术进行了高精度定年,测得凝灰岩层锆石206Pb/238U加权平均年龄为1368Ma±12Ma。进而结合区域资料讨论了锆石年龄的地质意义。该同位素年代学资料为华北青白口系下马岭组最新的资料,不仅准确地确定了地层的形成时代,而且对整个华北地台中、新元古代地层地质演化史的认识有着重要的意义。

Meso- and Neoproterozoic strata in North China have long been the main targets for the establishment of the late Precambrian stratotype in China and the chronostratigraphic position is a fundamental geological problem that the geoscience community has long paid attention to. However, many key horizons are still lacking in a highly precise isotopic age constraint. For the first time the authors obtained abundant magrnatic zircons in tufts of the Xiamaling Formation in the Qingbaikouan System in North China and used the SHRIMP Ⅱ technique to perform highly precise dating and obtained a weighted mean ^206Pb/^238U age of 1368±12 Ma for the zircons in tuff. Furthermore, the geological implications of this zircon age are discussed in combination with regional data. The isotope chronological data are the latest data of the Xiamaling Formation of the Qingbaikouan System in North China, which not only accurately indicate the age of the strata but also have great significance for the understanding of the geological evolution of the Meso- and Neoproterozoic strata in the whole North China platform.