新疆北部友谊峰一带喀纳斯群碎屑锆石U-Pb年龄及其对阿尔泰造山带构造演化的启示

Detrital zircon U-Pb age of the Kanas Group from the Friendship Peak region in northern Xinjiang and its implications for the tectonic evolution of the Altay Orogenic Belt

新疆北部阿尔泰山西段友谊峰一带发育的喀纳斯群碎屑沉积岩中保留了大量的古陆缘演化及沉积、变质等地质信息。采集了2个层位的碎屑锆石进行同位素年龄研究,结果显示:2套碎屑岩的锆石U-Pb年龄分布特征相近,最年轻的岩浆锆石年龄分别为546±4 Ma和545±4 Ma,代表了沉积时代的下限;较老的锆石年龄可分为太古宙的3063±16 Ma、2548±18 Ma和2541±18 Ma,古—中元古代的2223~1463 Ma,新元古代的985~781 Ma,据此推断,沉积物源存在前寒武纪结晶基底;较新的锆石变质年龄为421~429 Ma,与阿尔泰地区强烈的岩浆活动时间相近,可能与地层遭受后期的热液变质事件有关。结合地质构造演化,表明新疆北部地区大致经历了太古宙陆核形成阶段、Columbia超大陆形成和演化阶段、Rodinia超大陆汇聚和裂解阶段、震旦纪—寒武纪复理石沉积阶段,以及加里东期剧烈岩浆活动阶段。

A large amount of geological information about the evolution,sedimentation and metamorphism of paleo-continental margin is retained in fragment sedimentary rocks from the Kanas Group,which is developed in the Friendship Peak region in the western section of the Altay Mountains,northern Xinjiang.The detrital zircon samples were collected in two rock formations for the study of isotopic dating.The results showed that the distribution characteristics of zircon U-Pb age in the two sets of clastic rocks were similar.The youngest magmatic zircon ages were 546±4 Ma and 545±4 Ma,respectively,which represents the lower limit of the sedimentary age.The relatively older zircon ages can be divided into three categories:3063±16 Ma,2548±18 Ma and 2541±18 Ma in Archean Eon,2223~1463 Ma in Paleo-Meso Proterozoic Era,985~781 Ma in Neoproterozoic Era,which implies that the existence of Precambrian crystalline basement in the sediment source region.The relatively newer zircon age was 421~429 Ma,which is similar to the time of the strong magmatic activities in Altai region..It may be related to the stratum suffering from later hydrothermal deterioration events.The geological structure evolution in northern Xinjiang can be divided into five stages:the formation stage of the Archean continental nucleus,the formation and evolution stage of the Columbia supercontinent,the assembly and breakup stage of the Rodinia supercontinent,the deposition stage of Sinian-Cambrian flysch,the stage of severe magmatic activity in Caledonian.