扬子陆核的生长和再造:锆石U-Pb年龄和Hf同位素研究  

Growth and reworking of the Yangtze continental nucleus:evidence from zircon U-Pb ages and Hf isotopes

作　　者：张少兵[1] 郑永飞[1] 

机构地区：[1]中国科学技术大学地球和空间科学学院中国科学院壳幔物质与环境重点实验室,合肥230026

出　　处：《岩石学报》2007年第2期393-402,共10页Acta Petrologica Sinica

基　　金：国家自然科学基金(40334036)资助成果

摘　　要：对宜昌三峡附近崆岭杂岩中混合岩、片麻岩和变沉积岩以及莲沱砂岩进行了锆石U-Pb和Hf-O同位素研究,研究结果深化了我们对扬子陆核生长和再造的认识。在莲沱砂岩中发现了老达3.8Ga的碎屑锆石,说明扬子陆块可能存在这个年龄的地壳物质;其Hf同位素组成指示初生地壳生长出现在4.0Ga。崆岭杂岩中混合岩和片麻岩的U-Pb年龄表明,在3.2～3.3Ga和2.9～3.0Ga有两期重要的岩浆活动,指示扬子陆核可能于中太古代就开始形成。锆石Hf同位素研究则指示,其原岩至少从3.5Ga就开始从亏损地幔分异出来。混合岩和变沉积岩中所记录的1.9～2.0Ga变质事件,是扬子陆核再造并发生克拉通化的主要时期。而广泛分布于扬子陆块周边的新元古代岩浆活动不仅导致了许多太古宙和古元古宙地壳重熔,而且引起了初生地壳的快速再造。Abstract A combined study of zircon U-Pb and Hf-O isotopes was conducted on migmatite, gneiss and metpelite from the Kongling complex and the Liantuo sandstone at the Yangtze Gorge in Yichang. The results show great significance for growth and reworking of Yangtze continental nucleus. A detrital zircon as old as 3.8Ga was revealed by SHRIMP U-Pb dating for the Liantuo sandstone, implying the existence of crustal materials with this age in the Yangtze Block. Its Hf isotopes suggest growth of juvenile crust at 4.0Ga. Zircon U-Pb ages for the migmatite and gneiss from the Kongling complex suggest two episodes of magmatism at 3.2 ~ 3.3Ga and 2.9~ 3.0Ga, probably marking formation of Yangtze continental nucleus at Mesoarchean. Their Hf isotopes suggest extraction of protolith from the depleted mantle no later than 3.5Ga ago. Metamorphic event at 1.9 ~ 2. 0Ga is well recorded by the migmatite and metapelite, which may be the major episode for reworking of the nucleus and thus cratonization in the Yangtze Block. Neoproterozoic magmatism widely occurring in the periphery of the Yangtze Block caused not only remehing of Archean and Paleoproterozic ancient crust but also prompt reworking of juvenile crust.

关 键 词：扬子陆块 前寒武纪 大陆生长与再造 锆石U-PB年龄 锆石HF同位素 

分 类 号：P597.3[天文地球—地球化学]