扬子克拉通北部前泥盆纪地壳演化:来自碎屑锆石U-Pb和Hf同位素证据

Pre-Devonian crustal evolution of the northern Yangtze craton: evidence from U-Pb ages and Hf isotopes of detrital zircons

扬子克拉通前泥盆纪地壳演化过程一直是地学界研究的热点。本文报道了扬子克拉通北部武汉地区玉笋山剖面的志留系坟头组和泥盆系云台观组碎屑沉积岩中锆石U-Pb年龄和Hf同位素组成。结果表明,武汉地区坟头组和云台观组样品中最年轻的碎屑锆石年龄分别为430±5 Ma和415±5 Ma,将该地区坟头组和云台观组的沉积时代各限定在中志留世和晚泥盆世。碎屑锆石Hf同位素特点表明,沉积物源区在中太古代、新太古代以及新元古代形成了少量初生地壳,而古老地壳的再造主要发生在新太古代、新元古代和古生代,区域上最显著的初生地壳生长时期则是古元古代。综合对比扬子克拉通北部东、西两侧具有明显不同的锆石U-Pb年龄、微量元素和Hf同位素组成,暗示扬子克拉通可能由多个相对独立地壳演化过程的部分构成,而不具有统一的早前寒武纪基底。

The Pre-Devonian crustal evolution of the Yangtze craton has long been a hot topic in geosciences. This paper reports the zircon U-Pb ages and Hf isotopic compositions of the clastic sedimentary rocks of the Silurian Fentou Formation and the Devonian Yuntaiguan Formation in the Yusunshan section of the Wuhan area in the northern margin of the Yangtze craton. The results show that the youngest detrital zircons in the Fentou Formation and the Yuntaiguan Formation in Wuhan are 430±5 Ma and 415±5 Ma, respectively, limiting their sedimentary ages to the Middle Silurian and Late Devonian. Zircon Hf isotopic features reveal that their source area formed a small amount of juvenile crust in the Mesoarchean, Neoarchean and Neoproterozoic, while the reworking of the ancient crust mainly occurred in the Neoarchean, Neoproterozoic and Paleozoic. The most significant juvenile crustal growth period is Paleoproterozoic. By comprehensively comparing the zircon U-Pb ages, trace elements and Hf isotopic compositions of the eastern and western segments of the northern Yangtze craton, it is suggested that the Yangtze craton may be composed of a series of individual components which have their own crustal evolution processes, rather than a unified Early Precambrian basement.