摘要:
【目的】扬子西缘峨边群传统上被认为是华南中元古代晚期的代表性地层单元之一，其沉积时限与物源特征可为重建全球Rodinia超大陆汇聚背景下扬子陆块的中-新元古代构造演化过程提供重要约束。【方法】本文对峨边群变质碎屑沉积岩开展了岩石学和碎屑锆石U-Pb年代学分析，【结果】获得了峨边群枷担桥组两件变质细粒岩屑砂岩样品的碎屑锆石年龄区间为1950~900 Ma，主要相对概率峰值为 ~910 Ma、~1570 和~1730 Ma，以及次要峰值为~1130 Ma、~1390 Ma、~1840 Ma、~2500 Ma和~2550 Ma。最大沉积年龄分别为908 ± 8 Ma（MSWD = 0.10, n = 5）和905 ± 5 Ma（MSWD = 0.52, n = 9）。【结论】结合区域已有相关资料，峨边群枷担桥组的沉积时限为~910 Ma至~860 Ma，其沉积物源主要为扬子西缘的岩浆岩，主体方向为南侧，推测可能形成于新元古代早期微陆块拼合的构造背景，与Rodinia超大陆的全球性汇聚过程相关。
Abstract:
[Objectives] The Ebian Group in the western Yangtze Block has traditionally been regarded as one of the representative lithostratigraphic units of the late Mesoproterozoic in South China. The sedimentation age and provenance characteristics of Ebian Group can provide important constraints for reconstructing the Meso- Neoproterozoic tectonic evolution of the Yangtze Block under the background of the assembly of the global Rodinia supercontinent. [Methods] In this study, petrological and detrital zircon U-Pb geochronological analyses were conducted on metasedimentary rocks of the Ebian Group. [Results] The detrital zircon ages of two metamorphic fine-grained litharenite sandstones from the Jiadanqiao Formation of the Ebian Group range from 1950 to 900 Ma. The main relative probability peaks are ca. 910 Ma, ca. 1570 Ma, and ca. 1730 Ma, with secondary peaks at ca. 1130 Ma, ca. 1390 Ma, ca. 1840 Ma, and ca. 2500 Ma. The maximum depositional ages are 908 ± 8 Ma (MSWD = 0.10, n = 5) and 905 ± 5 Ma (MSWD = 0.52, n = 9), respectively. [Conclusion] Combining with regional geological data, the depositional age of the Jiadanqiao Formation of the Ebian Group is constrained to be 910~860 Ma. The sediment source was mainly from magmatic rocks in the western Yangtze Block, with a predominant direction towards the south side. It is speculated that the formation occurred during the early Neoproterozoic micro-block assembly and is associated with the global assembly process of the Rodinia supercontinent.
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