Provenance and tectonic setting of Neoproterozoic sedimentary sequences in the South China Block: evidence from detrital zircon ages and Hf–Nd isotopes
Provenance and tectonic setting of Neoproterozoic sedimentary sequences in the South China Block: evidence from detrital zircon ages and Hf–Nd isotopes
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DOI：
10.1007/s00531-011-0746-z
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发表时间：
2012-01
影响因子：
2.3
通讯作者：
Wei Wang;Fukun Chen;R. Hu;Y. Chu;Yi-Zeng Yang
中科院分区：
文献类型：
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作者：
Wei Wang;Fukun Chen;R. Hu;Y. Chu;Yi-Zeng Yang
华南陆块新元古代沉积序列为研究这一时期的构造演化和地壳增生提供了良好的机会。本文研究了扬子地块新元古代地层中碎屑锆石的U-Pb年龄、Hf同位素组成和全岩Nd同位素组成。碎屑锆石的年龄模式表明源区经历了2300 - 2560、1900 - 2100和770- 1000 Ma三个主要的岩浆活动期和2600 - 3400和770- 1000 Ma两个主要的年轻地壳增生期。古城冰川作用的最大年龄为768 Ma，可能与Kaigas冰川作用相对应，而不是Sturtian冰川作用。高La/Sc比值和低Cr/Th、Sc/Th、Co/Th比值表明，沉积岩主要来自长英质上陆壳源区，而εNd（t）和εHf（t）值变化较大，表明幔源岩浆岩也不同程度地为沉积序列提供了物质。全岩εNd（t）值和碎屑锆石U-Pb年龄谱的变化记录了弧后-弧后前陆-裂谷盆地的演化过程。新元古代序列中碎屑锆石的年龄分布与Rodinia主要地壳块体的年龄分布相比较表明，在Rodinia超大陆解体之前，扬子块体的位置可能与北方印度相邻，而不是在澳大利亚和劳伦大陆之间。
Neoproterozoic sedimentary sequences in the South China Block provide great opportunity to examine the tectonic evolution and crustal accretion during this period. This study presents U–Pb ages and Hf isotope composition of detrital zircons and Nd isotope composition of whole rocks of the Neoproterozoic sequences from the Yangtze Block, part of the South China Block. Age patterns of detrital zircons imply that the source area experienced three major periods of magmatic activity at 2,300–2,560, 1,900–2,100 and 770–1,000 Ma and two major episodes of juvenile crust accretion at 2,600–3,400 and 770–1,000 Ma. The maximum age of the Gucheng glaciation can be restricted at ~768 Ma from the youngest detrital zircon ages, probably corresponding to the Kaigas glaciation rather than to the Sturtian glaciation. High La/Sc ratio and low Cr/Th, Sc/Th and Co/Th ratios of the sedimentary rocks point to a derivation from dominantly felsic upper continental crustal sources, whereas large variation of εNd(t) and εHf(t) values indicates that mantle-derived magmatic rocks also provided material to the sedimentary sequences in different degrees. The shift in εNd(t) values of whole rocks and U–Pb age spectra of detrital zircons records the evolution from a back-arc to retro-arc foreland to a rift basin. Age distribution of detrital zircons from the Neoproterozoic sequences, compared with those of the major crustal blocks of Rodinia, implies that the position of the Yangtze Block was probably adjacent to northern India rather than between Australia and Laurentia before the breakup of the Rodinia supercontinent.