佛子岭群逆时针P-T轨迹对大别碰撞造山带构造演化的探究  

The anticlockwise P-T path from the Foziling Group:Constraint to the tectonic evolution of the Dabie orogen

作　　者：杨根山 石永红[1] 唐虎 李秋立[3,4] 侯振辉 YANG GenShan;SHI Yong Hong;TANG Hu;LI Qiu Li;HOU ZhenHui(College of Resources and Environmental Engineering,Hefei University of Technology,Hefei 230009,China;No.321 Geological Team Bureau of Geology and Mineral Exploration of Anhui Province,Tongling 244033,China;Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;College of Earth and Planetary Sciences,University of Chinese Academy of sciences,Beijing 100049,China;University of Science and Technology of China,Hefei 230009,China)

机构地区：[1]合肥工业大学资源与环境工程学院,合肥230009 [2]安徽省地质矿产勘查局321地质队,铜陵244033 [3]中国科学院地质与地球物理研究所,北京100029 [4]中国科学院大学地球与行星科学学院,北京100049 [5]中国科学技术大学,合肥230009

出　　处：《岩石学报》2020年第12期3654-3672,共19页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41972059)资助。

摘　　要：佛子岭群位于大别造山带最北缘,处于华北和扬子两大板块结合部位,构造位置十分关键,是解析两大板块精细耦合过程和探究大别造山带晚古生代构造事件的重要单元。然而,由于长期以来佛子岭群一直被视为"浅变质"复理石沉积单元,因而对其变质演化过程的解析较为薄弱,制约了对大别造山带形成过程的全面理解。本次通过对老虎场-龚店地质剖面细致的观测,石榴黑云母片麻岩精细的岩相学、矿物化学分析、热力学评价和年代学研究,建立了佛子岭群一个逆时针P-T变质演化型式。研究显示,佛子岭群记录了Ⅰ、Ⅱ、Ⅲ和Ⅳ四个变质阶段,温压变化依次为:(1)T=658~663℃、P=1.08~1.16GPa→(2)T=755~762℃、P=1.21~1.45GPa→(3)T=549~554℃、P=1.08~1.19GPa→(4)P标定=0.3~0.6GPa、T=477~499℃,(1)至(3)为近等压升温和降温过程,(3)至(4)则表现为近等温降压型式。锆石U-Pb定年显示了1484±64Ma^1180±192Ma、995±35Ma^606±14Ma和370±14Ma^331±8Ma三组年龄,前两组代表了碎屑锆石年龄;第三组共计7颗锆石,年龄集中,Th/U比值0.01~0.03,加权平均年龄为344±11Ma,代表了主期变质年龄。结合此次地质剖面结构特征和岩石类型,以及前人白云母40Ar-39Ar的270~255Ma变质年龄,表明佛子岭群记录了两期变质事件,早期为晚古生代的拉张背景下的岛弧根部变质,晚期为晚古生代末的较为快速抬升构造热事件,并据此推测大别造山带可能为增生和碰撞复合型造山带。The Foziling Group(FZG)is located in the northernmost margin of the Dabie orogen,at the junction of the North China and the Yangtze plates,which occupies the pivotal tectonic position,and is an important unit for analyzing the subtle coupling process of the two plates and probing the Late Paleozoic tectonic events of the Dabie orogen.However,the FZG has long been regarded as a"lower-grade metamorphic"flysch sedimentary unit,so the analysis of its metamorphic evolution is relatively weak,which restricts the comprehensive understanding of the formation process of Dabie orogen.Based on the careful fieldtrip of the geological profile across Laohuchang-Gongdiang,and the fine petrological observation,mineral chemical analysis,thermodynamic evaluation and chronology research for the garnet-biotite gneiss,a anticlockwise P-T path has been established for the FZG.Four metamorphicⅠ,Ⅱ,ⅢandⅣ-stages have been displayed in the FZG,and the temperature and pressure varies in sequence as follows:(1)T=658~663℃and P=1.08~1.16 GPa→(2)T=755~762℃and P=1.21~1.45 GPa→(3)T=549~554℃and P=1.08~1.19 GPa→(4)P-calibration=0.3~0.6 GPa and T=477~499℃.The near-isobaric warming and the near-isobaric cooling have been shown from(1)to(3),respectively.The near-isothermal depression has been defined between(3)and(4).The ages of the three groups have been confirmed as1484±64 Ma^1180±192 Ma,995±35 Ma^606±14 Ma and 370±14 Ma^331±8 Ma by the U-Pb dating of the zircons.The first two groups represent the ages of the detrital zircons,while the third group contains a total of seven zircons with concentrated ages and Th/U ratio of 0.01~0.03,the weighted average age is 344±11 Ma,representing the age of the main metamorphism.Combined with the construction and the rock type in this the geological profile,and the previous 270~255 Ma metamorphic age of the muscovite40 Ar-39 Ar,the FZG has recorded two metamorphic events,the early event has reflected the root metamorphism of island arc under tension background at the Late Paleozoic,and

关 键 词：佛子岭群 浅变质 逆时针P-T轨迹 锆石U-PB 岛弧拉张环境 

分 类 号：P588.345[天文地球—岩石学] P597.3[天文地球—地质学]