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在祁连造山带东端古元古界陇山岩群中新识别出中元古代长宁驿花岗质片麻岩。为了精确确定长宁驿花岗质片麻岩的形成时代,对其进行了激光等离子体质谱LA-ICP-MS单颗粒锆石微区U-Pb同位素测年,花岗质片麻岩中锆石Th/U比值介于0.50～2.09,阴极发光图像显示锆石内部发育典型的岩浆生长震荡环带结构,属于岩浆结晶的产物。测得花岗质片麻岩的原岩岩浆结晶年龄为1765Ma±57Ma,表明该花岗质片麻岩原岩的形成时代为中元古代早期,可能形成于华北板块经吕梁运动后的后造山环境中,同时还从捕获的继承性岩浆锆石中得到了时代为1.95Ga、2.20Ga左右的继承年龄。结合区域地质资料,综合分析研究后认为,在中元古代祁连地块仍为华北板块西南缘的一部分,两者之间具有相同的结晶基底和构造属性,它们共同经历了吕梁运动后的后造山和陆内伸展裂解阶段,很可能与Columbia超大陆的聚合和裂解相关。
In the eastern Qilian orogenic belt in the ancient Paleocene Longshan rock group newly identified in the Middle Proterozoic granite gneiss. In order to accurately define the formation age of granitic gneiss in Changning, the zircon U-Pb isotope dating of LA-ICP-MS single grain zircon grains in the granitic gneisses was studied by laser plasma-mass spectrometry. Th / U ratio ranged from 0.50 to 2.09. The cathodoluminescence image shows the typical magma growth oscillatory zone developed within the zircon and belongs to the product of magma crystallization. The original magmatic age of granitic gneisses is 1765Ma ± 57Ma, indicating that the granitic gneiss was formed in the early Mesoproterozoic and probably formed in the post-orogenic environment after the Lvliang movement of the North China Plate In the meantime, the succession ages of 1.95Ga and 2.20Ga were obtained from the inherited magmatic zircons. Combined with the regional geological data, a comprehensive analysis shows that the Qilian block in the Proterozoic is still a part of the southwestern margin of the North China Plate, and has the same crystalline basement and tectonic attribute between the two. Together, they experienced Luliang motion The orogenic and intracontinental extensional pyrolysis stages are most likely associated with the polymerisation and pyrolysis of the Columbia continent.