吉林敦化地区万宝岩组碎屑锆石U-Pb-Hf同位素组成:对区域构造演化的制约  

U-Pb-Hf Isotopic Compositions of Detrital Zircons from Wanbao Formation in Dunhua Area of Jilin:Constraints on Regional Tectonic Evolution

作　　者：关子成 裴福萍[1] 魏敬洋 李鹏屹 Guan Zicheng;Pei Fuping;Wei Jingyang;Li Pengyi(College of Earth Sciences,Jilin University,Changchun 130061,China)

机构地区：[1]吉林大学地球科学学院,长春130061

出　　处：《吉林大学学报（地球科学版）》2024年第4期1264-1279,共16页Journal of Jilin University：Earth Science Edition

基　　金：国家自然科学基金项目(41972053);吉林大学2022年研究生创新研究计划项目(2022196)。

摘　　要：为制约古亚洲洋在吉林东部地区的最终闭合时间,本文选取吉林省敦化地区万宝岩组变质粉砂岩为研究对象,开展系统的碎屑锆石微量元素组成和U-Pb-Hf同位素研究,确定了万宝岩组的沉积时限和物源区特征,并通过碎屑锆石微量元素获得晚古生代地壳厚度的变化规律,探讨了华北板块北缘东段晚古生代的构造演化历史。万宝岩组由互层的大理岩、变质粉砂岩和变质细砂岩组成,碎屑锆石定年结果显示,万宝岩组最年轻峰值年龄约为316 Ma,此外还存在355、398、1 842和2 360 Ma的峰值年龄。其中,古生代碎屑锆石(409~312 Ma)以具有负的εHf(t)值(-15.32~-1.60)及新太古代—古元古代的TDM2年龄(2 293~1 480 Ma)为特征,侵入万宝岩组闪长岩体的时期为276 Ma。综合研究认为,敦化地区万宝岩组沉积时限为312~276 Ma,即早二叠世时期,其沉积时限和岩石组合特征可与延边地区的庙岭组相对比。万宝岩组中的古生代碎屑锆石来自华北板块太古宙—古元古代结晶基底物质的部分熔融。结合其中古元古代碎屑锆石(62.9%)的大量出现,暗示敦化地区或/和附近地区存在华北板块前寒武纪的结晶基底。通过地壳厚度计算表明,敦化地区和内蒙古地区晚古生代的地壳厚度变化趋势一致,说明二者晚古生代的演化历史趋于同步。约245 Ma地壳厚度达到最大(80 km),暗示了古亚洲洋的最终闭合。In this paper,the metamorphic siltstones of the Wanbao Formation in Dunhua,Jilin Province,were studied.The research included detailed analysis of detrital zircon trace elements and U-Pb-Hf isotopes to determine the sedimentary timeframe and source characteristics of the Wanbaoyan Formation.Further,the variation pattern of Late Paleozoic crustal thickness,inferred from detrital zircon trace elements,was used to explore the Late Paleozoic tectonic evolution history of the eastern part of the Northern margin of the North China plate.The Wanbao Formation consists of interbedded marble,metamorphic siltstone and metamorphic fine sandstone.The detrital zircon dating results show that the youngest peak age of the Wanbao Formation is~316 Ma,in addition to peak ages of 355 Ma,398 Ma,1842 Ma and 2360 Ma.The Paleozoic detrital zircons(409-312 Ma)have negativeεHf(t)values(-15.32--1.60)and a T DM2 age(2293-1480 Ma)in the Neo-Paleozoic-Paleozoic period,with the age of the amphibolite bodies intruding Wanbao Formation is 276 Ma.The comprehensive study concludes that the depositional timeframe of Wanbao Formation in Dunhua area is 312-276 Ma,i.e.,the Early Permian period,and shares similarities in depositional timeframe and rock assemblage characteristics with the Miaoling Formation in Yanbian area.The Paleozoic detrital zircons in Wanbao Formation are derived from partial melting of materials from the Paleozoic-Tertiary crystalline basement of the North China plate.Furthermore,the prevalence of Precambrian detrital zircons(62.9%)implies the presence of Precambrian crystalline basement of the North China plate in or near the Dunhua area.The crustal thickness calculation shows a similar trend in Late Paleozoic crustal thickness between Dunhua and Inner Mongolia regions,indicating synchronized evolutionary histories.The crust reached its maximum(80 km)thickness at~245 Ma,suggesting the final closure of the Paleo-Asian Ocean.

关 键 词：华北板块北缘 晚古生代 碎屑锆石 U-Pb-Hf同位素 地壳厚度 万宝岩组 古亚洲洋 

分 类 号：P597[天文地球—地球化学] P56[天文地球—地质学]