吉林省敦化市东石河林场正沟岩组地球化学和碎屑锆石年代学特征

Geochemistry and debris zircon chronological features of Zhenggou formation complex in Dongshihe forest farm of Dunhua City,Jilin Province

吉林省敦化东石河地区的正沟岩组,其成岩时代及变质时代一直是研究的重点。利用地球化学特征及不同层位岩石之间的相互关系,并结合碎屑锆石U-Pb年代学结果共同限定了本区正沟岩组的沉积时限及变质时代,通过原岩恢复表明,正沟岩组原岩大多是中酸性火山岩及其相应的火山碎屑岩,其余为泥砂质或钙质沉积岩,属于火山-沉积岩建造。原岩构造环境特征,反映了陆缘向陆内构造演化的特征,同时也反映了变质流纹岩的原岩形成时代较砂质板岩与变质砂岩的原岩要晚。锆石U-Pb测年结果显示,岩浆锆石加权平均年龄为297.6Ma,确定其成岩时代为早二叠世。那么其变质时代必然较晚。变质锆石的加权平均年龄为181.6 Ma。因此我们将正沟岩组的变质时代厘定为早侏罗世。

The diagenetic age and metamorphic age of the Zhenggou formation complex the Dongshihe area of Dunhua, Jilin Province have been the focus of the study. Using the geochemical characteristics and the interrelationships between different layers of rocks, combined with the debris zircon U-Pb chronological results, the sedimentary time and metamorphic age of the positive ditch group are defined. The main rocks of the ditch rock are mostly middle-acid volcanic rocks and their corresponding volcanic clastic rocks, and the rest are muddy or calcareous sedimentary rocks, belonging to volcanic-sedimentary rocks. The characteristics of the original rock tectonic environment reflect the evolution of the continental margin to the tectonic evolution, but also reflect the late rock formation of the metamorphic rhyolite and the later of the original rock of the sandstone and metamorphic sandstone. The zircon U-Pb dating results show that the weighted average age of magmatic zircon is 297.6Ma, and the diagenetic age is the Lower Permian. Then its metamorphic age must be late. The weighted average age of metamorphic zircon is 181.6Ma. Therefore, we define the metamorphic age of the ditch formation complex as the Lower Jurassic.