吉林果松盆地早白垩世果松组火山岩年代学及其地质意义

以果松盆地果松组火山岩为研究对象,对标准剖面安山岩进行了精确的锆石U-Pb定年分析,旨在确定其形成时代。样品中的锆石多呈自形-半自形晶,振荡环带发育,Th/U比值在0.48~2.77之间,显示其典型的岩浆成因。锆石U-Pb定年结果显示,原定中晚侏罗世的果松组火山岩形成于130 Ma(加权平均年龄为130±2 Ma,MSWD=0.48)或129 Ma(加权平均年龄为129±2 Ma,MSWD=0.14),应划归为早白垩世。根据果松盆地中生界岩石组合特点,结合新获得的火山岩测年数据和生物化石种群特征,重新厘定果松盆地中生代地层序列,进而讨论了果松盆地与邻区白垩纪地层单元的地层对比关系。

Geochronology and geological significance of Early Cretaceous volcanic rocks from Guosong Formation in Guosong Basin,Jilin

Taking the volcanic rocks from Guosong Formation in the Guosong Basin as research objects, accurate zircon U-Pb dating for the andesites of the typical section is undertaken to determine the formation age of the volcanic rocks. Most zircons of the selected samples are euhedral-subhedral in shape, and display distinct oscillatory zoning structures. The values of Th/U range in 0.48~2.77, implying a typical magmatic origin. Zircon U-Pb dating shows that the previous defined Mid-Late Jurassic Guosong Formation volcanic rocks actually formed in 130 Ma (weighted mean age is 130±2 Ma, MSWD=0.48) or 129 Ma(weighted mean age is 129±2 Ma, MSWD=0.14) and should be grouped into the Early Cretaceous. Based on the composition of the Mesozoic rock assemblage in Guosong Basin and combined with newly acquired zircon U-Pb dating and characteristics of fossil assemblages, the Mesozoic stratigraphic sequence in Guosong Basin has been redefined, and the stratigraphic correlation of the Cretaceous units in the Guosong Basin with adjacent areas has been investigated.