Stratigraphic Division And Correlation Of The Early Cretaceous Volcanic Rocks In Caozhuang Area Of Xingcheng, Western Liaoning

This paper selected the early Cretaceous volcanic of Caozhuang area as the research object. The author determined the volcanic-sedimentary sequence, through large scaled investigation in this area and the sectionⅠ(SⅠ) measuring. According to the LA-ICP-MS zircon U-Pb dating and the geochemical analyses of the typical rock samples of Xingcheng area, and combining with the section Ⅱ(SⅡ) of Xintaimen basin, the author proposed that the Yixian Formation in Xingcheng area can be regarded as the type section of Yixian Fomation. The study contents and results contain the following aspects:1.The field works contain the large scaled investigation in research area and the sectionⅠ(SⅠ) measuring. The author determined the volcanic-sedimentary sequence of early Cretaceous in Caozhuang area and divided the Yixian Formation part into two members(K1y1 and K1y2) based on arraging and analyzing the regional rock association characteristics.2.The weighted average ages of LA-ICP-MS zircon U-Pb dationg for five typical rock samples are 131.5±1.4Ma, 126.0±1.2Ma, 129.2±1.0Ma, 113.3±1.6Ma and 112.7±2.6Ma, respectively. The result shows that the ages of the rock samples in Jianshan-Wuliqiao quarry consistent with the age obtained from Yixian Formation, though the ages of the rock samples in Laotan area are younger. It indicates that the strata in Laotan area can be regarded as the lava facies of Jiufotang Formation or Fuxin Formation.. The contact between them is unconformity, and they are forming by different volcanic activities of early Cretaceous in the south of western Liaoning.3.Taking the correlation with the volcanic-sedimentary sequences, the author proposes that the Yixian Formation in Caozhuang area can be regarded as the lower and middle Yixian Formation in the type section, and the Yixian Formation in Xintaimen basin can be regarded as the lower member(K1y1) in Caozhuang area.4.The geochemical analyses result of the major elements, trace elements and rare earth elements of two types rock samples from Jianshan area and Laotan area showed that the volvanic rock in Jianshan area were high-K calc-alkaline series, been shoshonites series in Laotan area,, they had a common source(crust-mantle mixing source and they were generated in response to lithosphere extension.