大别山造山带宿松岩群锆石U-Pb年龄和Nd同位素特征:宿松地体物源和属性  

Zircon U-Pb Ages and Nd Isotopic Characteristics of Susong Group in Dabie Orogenic Belt:Source and Provenance of Susong Terrene

作　　者：李俊辉[1] 于洋[1] 韦龙猛 胡昭平[1] 陈福坤[1] 

机构地区：[1]中国科学技术大学地球和空间科学学院,安徽合肥230026

出　　处：《地球科学与环境学报》2016年第1期21-33,共13页Journal of Earth Sciences and Environment

基　　金：国家自然科学基金项目(40973042;41090372)

摘　　要：大别超高压变质造山带南部的宿松地体主要由高压变质宿松岩群或杂岩组成,其岩性和物源构成复杂,历来的研究颇具争议。报道了宿松岩群的片麻岩、片岩和变质基性岩石等主要岩石类型的锆石U-Pb年龄和Nd同位素组成,限定了岩石地球化学特征,探讨了宿松地体的属性及地壳演化。两个片麻岩样品的锆石U-Pb同位素年龄为750 Ma至约770 Ma,初始εNd值为-7.3^-1.6,可以推测原岩为新元古代岩浆岩;两个片岩样品的碎屑锆石U-Pb年龄值分布范围较大,并主要集中于晚太古代(2 700Ma至约2 800 Ma)、早元古代(2 000 Ma至约2 500 Ma)、中元古代(1 100 Ma至约1 500Ma)和新元古代(700Ma至约800Ma),推测原岩为新元古代沉积岩。片岩的Nd同位素组成变化较大,初始εNd值(回扣至750 Ma)为-20.2^-1.4,暗示剥蚀区的物质组成复杂。相似的碎屑锆石U-Pb年龄分布特征也普遍地记录在扬子陆块的基底岩石或沉积盖层中。新元古代岩浆岩广泛分布于宿松岩群、大别—苏鲁造山带超高压变质地体乃至扬子陆块边缘,指示宿松高压变质地体具有扬子陆块属性和相似的地壳演化历史。Susong Group or Susong rock complex is the major rock unit of Susong terrene in the southern part of Dabie ultrahigh-pressure orogenic belt.Rocks of this group undergo highpressure metamorphism and have complex origins or sources,and hence,the provenance and evolution history of Susong terrene are still debated.Zircon U-Pb ages and whole-rock Nd isotopic data for gneisses,schists and metabasic rocks of Susong Group were presented to place geochemical characteristics of Susong Group,and the evolution of the crust and provenance of Susong terrene were discussed.Zircons separated from two gneiss samples yield U-Pb ages of 750to^770 Ma,suggesting as evidence for a magmatic event in Neoproterozoic.InitialεNdvalues of whole-rocks of the gneisses range from-7.3to-1.6.Detrital zircons from two schist samples give a wide range of U-Pb ages,clustering around Late Archean（2 700 Ma to ~2 800 Ma）,Paleoproterozoic（2 000 Ma to ~2 500 Ma）,Mesoproterozoic（1 100 Ma to ~1 500 Ma）andNeoproterozoic（700to ~800 Ma）,implying Neoproterozoic sedimentary rocks as their protoliths.InitialεNdvalues of whole-rocks of the schists vary from-20.2to-1.4,when calculated back to750 Ma,suggesting complex rock components in the source area.Similar distribution patterns of detrital zircon U-Pb ages are also commonly recorded in the basement or sedimentary cover rocks exposed in Yangtze Block.The Neoproterozoic magmatic rocks are widely distributed in Susong Group,ultrahigh-pressure metamorphic terrenes of Dabie-Sulu orogenic belt and the continental margins of Yangtze Block,indicating that Susong high-pressure metamorphic terrene is of a Yangtze affinity and has had similar history of the crustal evolution.

关 键 词：地壳演化 构造属性 前寒武纪 U-Pb年龄 ND同位素 宿松岩群 扬子陆块 大别造山带 

分 类 号：P597[天文地球—地球化学]