华北克拉通五台绿岩带锆石年代学及地质意义  

Zircon geochronology and geological implications of the Wutai greenstone belt,North China Craton

作　　者：李秋根[1] 黄萧 初航 孙迪 刘文煜 LI QiuGen;HUANG Xiao;CHU Hang;SUN Di;LIU WenYu(Key Laboratory of Orogenic Belts and Crustal Evolution,Ministry of Education,School of Earth and Space Sciences,Peking University,Beijing 100871,China;Tianjin Center,China Geological Survey(North China Center for Geoscience Innovation),Tianjin 300170,China;Research Institute Ltd.of China National Offshore Oil Corporation,Beijing 100028,China)

机构地区：[1]造山带与地壳演化教育部重点实验室,北京大学球与空间科学学院,北京100871 [2]中国地质调查局天津地质调查中心(华北地质科技创新中心),天津300170 [3]中海油研究总院有限责任公司,北京100028

出　　处：《岩石学报》2024年第11期3426-3447,共22页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(42172215、41372193、41530207)资助.

摘　　要：五台花岗-绿岩带位于华北克拉通中部造山带的中心地区,保存有较完整的地质记录,并赋存条带状铁建造(BIFs)型铁矿,一直是研究的热点地区之一。然而,该绿岩带尚需详细年代学研究来重新厘定其岩石地层划分。本文对该区域三个组,即金岗库组、柏枝岩组和鸿门岩组中发育的变质火山岩开展了锆石U-Pb年代学和Lu-Hf同位素组成分析。锆石U-Pb定年结果显示,五台花岗-绿岩带五台群中的金岗库组、柏枝岩组和鸿门岩组的变质火山岩喷发年龄分别为2540±8 Ma、2524~2530 Ma和2513~2517 Ma,同时还记录了~2700 Ma的继承年龄和1930~1853 Ma的变质年龄。锆石Lu-Hf同位素分析结果显示它们的εHf(t)值分别为+0.4~+5.5、+1.2~+7.5和+2.2~+10.5,相应的亏损地幔模式年龄为2639~2845 Ma、2546~2788 Ma和2425~2752 Ma,εHf(t)值呈现大的变化且增加的趋势。结合前人的研究,本文确定了五台群中的金刚库组、庄旺-文溪组、柏枝岩组和鸿门岩组分别形成于~2540 Ma、~2530 Ma、~2525 Ma和~2515 Ma,它们记录了四期火山活动,说明五台绿岩带中的表壳岩系尽管经历了变形变质作用的改造依然保存了较完整的地层层序序列,并提出回撤-前进式俯冲-底冲演化模型。这些结果对理解五台花岗-绿岩带乃至华北克拉通新太古代-古元古代构造及演化具有重要意义。The Wutai greenstone belt,located in the central area of Trans-North China Orogen in the North China Craton(NCC),contains relatively well-preserved geological signatures,with occurrence of widespread economic BIFs deposits,and has been one of the research hotspots.However,due to lack of detailed geochronological data,a rigorous understanding of its lithostratigraphic divisions is yet to be well established.In this paper,detailed zircon U-Pb-Hf analysis of metamorphic volcanic rocks from three formations,namely,the Jingangku,Baizhiyan and Hongmenyan formations,were performed.Zircon U-Pb dating results yield eruption ages of 2540±8 Ma,2524~2530 Ma and 2513~2517 Ma from the magmatic zircon grains of the three formations,respectively,together with inherited zircon ages of~2700 Ma and metamorphic ages of 1930~1853 Ma.The analysis results of zircon Lu-Hf isotopes of the Jingangku,Baizhiyan,and Hongmenyan formations show theirεHf(t)values range from+0.4 to+5.5,from+1.2 to+7.5 and from+2.2 to+10.5,corresponding to their depleted mantle model ages(tDM)of 2639~2845 Ma,2546~2788 Ma and 2425~2752 Ma,respectively,signifying large variation and increasing trend of theεHf(t)values with the eruption time.According to the previous data,four episodes of the volcanic activities from the Wutai Group are recognized:~2540 Ma,~2530 Ma,~2520 Ma and~2515 Ma,corresponding to the Jingangku,Zhuangwang-Wenxi,Baizhiyan and Hongmenyan formations respectively,which are orderly deposition from bottom to up,and constitute a relatively complete stratigraphic sequence,despite modification of multiperiod metamorphism and deformation.As a result,a probable retreating-advancing subduction-underthrusting tectonic scenario is proposed.These results can provide a better understanding for the development of the Wutai granite-greenstone belt,and even the fundamental tectonic evolution of the Neoarchean-Paleoproterozoic era of the NCC.

关 键 词：U-PB年代学 LU-HF同位素 变质火山岩 花岗-绿岩带 华北克拉通 

分 类 号：P588.14[天文地球—岩石学] P597.3[天文地球—地质学]