甘肃北山小草湖火山岩系形成时代的重新厘定

甘肃北山小草湖一带敦煌岩群的北侧分布着一套发生韧性变形的火山岩系(前人称之为小草湖岩片)。该火山岩系的宏观岩貌、岩石学、岩石地球化学等特征与相邻的二叠纪火山岩系相似,为大陆裂谷火山岩系列。本次研究在糜棱岩化英安岩中获得285Ma±4Ma的LA-ICP-MS单颗粒锆石微区U-Pb同位素年龄,证明该火山岩系的时代并非志留纪,而是二叠纪,属于天山石炭纪—二叠纪大火成岩省的组成部分。这一新资料对甘肃北山构造格局及其演化历史的研究具有重要意义。

The re-definition of formation age of Xiaocaohu volcanic rocks in Beishan area, Gansu Province, China

Xiaocaohu rock sheet developed in north of Dunhuang Group in Beishan Xiaocaohu area of Gansu Province, and the volcanic association exhibited sharply ductile deformation. Xiaocaohu rock sheet is similar to Permian volcanic association in terms of petrographic geomorphology, petrology and lithogeochemistry, and it belongs to rift-related volcanic rocks. Through LA-ICP-MS zircon U-Pb dating, we have obtained the isotopic age of 285±4Ma from the mylonitization dacite. The result proves that Xiaocaohu volcanic association is not a product derived from magmatism activities of Silurian but Permian, and it is a component of Carboniferous-Permian large igneous provinces in Tianshan area. The new information is of great significance to further study tectonic framework and evolution of Beishan area, Gansu Province.