大别地区构造与地壳演化——来自河流碎屑锆石U⁃Pb⁃Hf同位素的制约

Tectonic and Crustal Evolution in the Dabie Area:Constraints from U-Pb-Hf isotopes of river clastic zircons

【目的与方法】为系统揭示大别地区经历的岩浆构造热事件及地壳生长历程,对大别地区3条不同河流碎屑沉积物中的锆石开展U-Pb-Hf同位素分析。【结果】锆石U-Pb年龄可分为4组:2676~2424 Ma、2035~1812 Ma、890~748 Ma、140~120 Ma。锆石Hf二阶段模式年龄(tDM2)亦可分为4组:3371~3241 Ma、2470~2329 Ma、1858~1751 Ma和1132~1072 Ma。【结论】(1)大别地区记录的岩浆活动可大致分为9个阶段,分别为4.00~3.00 Ga、2.90~2.40 Ga、2.10~1.80 Ga、0.90~0.70 Ga、0.14~0.12 Ga的“爆发期”,与3.00~2.90 Ga,2.40~2.10 Ga,1.80~0.90 Ga,0.70~0.14 Ga的“平静期”;(2)大别地区主要经历了4期构造热事件,分别发生在新太古代晚期(~2.50 Ga)、古元古代中期(~2.00 Ga)、三叠纪(0.24~0.20 Ga)与白垩纪(0.14~0.12 Ga);(3)大别地区主要经历4期显著的地壳生长,地球形成初期约4.4~4.1 Ga地壳初始生长、4.0~2.8 Ga地壳快速生长累积、2.6~2.0 Ga持续地壳生长与2.0 Ga以来地壳缓慢生长,大别地区2.7~2.4 Ga的岩浆活动十分强烈,说明该时期地壳再造事件也十分普遍;(4)~2.0 Ga之前大别与黄陵地区岩浆、变质、地壳生长事件存在明显差异,表明在此之前两者更可能为独立的微陆块。

[Objective and Methods]This study aimed to systematically reveal the magmatic tectonic thermal events and crustal growth processes experienced in the Dabie area,U-Pb Hf isotope studies were conducted on zircons from three different river debris sediments in the Dabie area[.Results]The results showed that zircon U-Pb ages can be divided into four groups:2676-2424 Ma,203-1812 Ma,890-748 Ma,and 140-120 Ma.The zircon Hf two-stage model age(tDM2)can also be divided into four groups:3371-3241 Ma,2470-2329 Ma,1858-1751 Ma,and 1132-1072 Ma.[Conclusions](1)The magmatic activity records in the Dabie region can be roughly divided into nine stages.The"quiet periods"are 3.00-2.90 Ga,2.40-2.10 Ga,1.80-0.90 Ga,and 0.70-0.14 Ga respectively,and the"explosive periods"are 4.00-3.00 Ga,2.90-2.40 Ga,2.10-1.80 Ga,0.90-0.70 Ga,and 0.14-0.12 Ga.(2)The Dabie area has experienced four metamorphic events,which occurred in the Late Neoarchean(~2.50 Ga),Middle Paleoproterozoic(~2.00 Ga),Triassic(0.24-0.20 Ga),and Cretaceous(0.14-0.12 Ga).(3)The Dabie area mainly experienced four stages of crustal growth:the initial growth of the Earth's crust was approximately 4.4-4.1 Ga in the early stage of Earth formation;there was rapid growth and accumulation of crust from 4.0-2.8 Ga;2.6 Ga to 2.0 Ga experienced long-term crustal growth,with strong the magmatic activity at 2.7 Ga to 2.4 Ga in the Dabie area,indicating that crustal reconstruction events were also extremely common during this period;crust grew slowly after 2.0 Ga.(4)Before 2.0 Ga,there were significant differences in magma,metamorphism,and crustal growth events between the Dabie and Huangling areas,indicating that the two were more likely independent micro blocks before this.