河南鲁山地区太华杂岩LA-ICP-MS锆石U-Pb年代学及其地质意义

摘要

As the largest and oldest craton in China,the North China Craton is an ideal region for investigating the magmatic activity and tectonic evolution of Archean period,and hence has attracted considerable interest among geologists in China.The Taihua complex is an important part of the North China Craton,distributed in WWN-EES direction along its southern margin.In this study,the authors chose the Taihua complex in the Lushan area as the study object,investigated geological section in detail,and revealed formation age,metamorphic events age by LA-ICP-MS zircon U-Pb dating.Zircon U-Pb dating of the amphiboite yielded the weighted mean 207Pb/206Pb ages of 2 788 ± 16 Ma,2 714 ± 12 Ma,and 1 920 ± 18 Ma,which represent the formation age of the amphiboite,first stage metamorphic age,and second stage metamorphic age,respectively.Together with previous work about zircon U-Pb dating and Hf isotope,the authors analyzed and discussed the geological significance of the three geological events:2 850～2 700 Ma is an important period of magmatic event,and represents the formation of Archean new crust;2 800 ～ 2 600 Ma and ～ 1 900 represent the two metamorphic events and suggest that the Taihua complex was subjected to Neoarchean and Paleoproterozoic metamorphic alteration.The results obtained by the authors not only contribute to the interpretation of the formation age and the age of the metamorphic events of the Taihua complex and their geological significance but also provide new data for the further study of the formation and evolution of the southern margin of North China Craton and the whole North China Craton.%华北克拉通是我国最大且最古老的克拉通,是研究太古宙岩浆活动和构造演化的理想区域,一直备受地质学家的关注.太华杂岩是华北克拉通的重要组成部分,主要分布在其南缘,总体呈近北西西-南东东向分布.在详细野外地质调查的基础上,对鲁山地区太华杂岩中的斜长角闪岩样品进行了LA-ICP-MS锆石U-Pb定年,以揭示其成岩及变质事件时代.样品的锆石U-Pb加权平均207Pb/206Pb年龄为2 788±16、2 714±12和1 920±18 Ma,分别代表斜长角闪岩成岩年龄、早期变质事件年龄及晚期变质事件年龄.综合梳理前人的锆石U-Pb年代学及Hf同位素研究数据,分析并讨论了3次地质事件的地质意义:2 850～2 700 Ma为一期重要的岩浆事件,代表了太古宙新生地壳的形成;2 800～2 600和～1 900 Ma为两期变质事件,期间太华杂岩分别遭受新太古代和古元古代两次变质变形改造.本次研究不仅可以解释太华杂岩的形成、变质时代及其地质意义,而且为进一步研究华北克拉通南缘乃至整个华北克拉通的形成与演化过程提供了新的数据资料.