ABSTRACT

The Neoproterozoic Zhoutan Group, located at the conjunction area between the Yangtze and the Cathaysia Blocks, preserves an important record of the Neoproterozoic sedimentary system of the South China Block. However, its accurate depositional age, provenance, and tectonic affinity remain poorly studied. Here, we report new LA-ICP-MS detrital zircon U–Pb age data of four meta-sedimentary samples from the Zhoutan Group in the Nancheng area for complemental decipherment of its sedimentary and tectonic histories. Concordant detrital zircon ages reveal proportions of 54% latest Mesoproterozoic to early Neoproterozoic (ca. 1050–820 Ma), 24% early Paleoproterozoic (ca. 2500–2150 Ma), and 22% late Paleoproterozoic to early Mesoproterozoic (ca. 2000–1500 Ma) populations. Youngest detrital zircon age clusters exhibit a consistent weighted mean age of ca. 827 Ma, suggesting the maximum Tonian depositional age of the Zhoutan Group. Provenance interpretations reveal that the detritus of investigated samples were mainly sourced from the proximal Jiangnan Orogen with some additionally derived from the Cathaysia Block, the interior Yangtze Block, and/or extraneous terranes. In addition, the appearance of some later early Palaeozoic-aged (ca. 437 Ma) metamorphic rims and grains suggest that the Zhoutan Group has locally experienced an intense metamorphism during the early Palaeozoic (Silurian) time, which has been consistently recorded by the Neoproterozoic meta-strata in the Cathaysia Block. These new data, together with those from previous studies, indicate that the Zhoutan Group belongs to the early Neoproterozoic sedimentary successions between the Yangtze and the Cathaysia Blocks. Subsequently, it might be thrusted onto the present side of the Cathaysia Block during later tectonic processes and was affected by locally metamorphism during the Silurian time. Thus, such observations suggest that the potential border between the Yangtze and the Cathaysia Blocks should be to the north of the current position of the Zhoutan Group.

摘要

位于扬子地块与华夏地块交汇处的新元古代周滩群，保存着华南地块新元古代沉积体系的重要记录。然而，其准确的沉积年龄、来源和构造亲和力仍然缺乏研究。在这里，我们报告了来自南城地区周滩群的四个变质沉积样品的新 LA-ICP-MS 碎屑锆石 U-Pb 年龄数据，以对其沉积和构造历史进行补充破译。一致碎屑锆石年龄显示 54% 的最新中元古代至早新元古代（约 1050-820 Ma），24% 的早古元古代（约 2500-2150 Ma），和 22% 的晚古元古代至早中元古代（约 1000-100-1000 年 5 月）马）人口。最年轻的碎屑锆石年龄簇表现出一致的加权平均年龄约。827 Ma，表明周滩群的最大托期沉积时代。物源解释表明，被调查样品的碎屑主要来自近江南造山带，另外一些来自华夏地块，扬子内部和/或外部地层。此外，一些晚古生代（约437 Ma）变质边缘和颗粒的出现表明，周滩群在早古生代（志留纪）局部经历了强烈的变质作用，新元古代一直有记录。华夏地块的元地层。这些新资料与以往研究资料一起表明，周滩群属于扬子地块和华夏地块之间的早新元古代沉积序列。随后，它可能在后期的构造过程中被推到华夏地块的现在一侧，并在志留纪时期受到局部变质作用的影响。因此，这些观察结果表明，长江与华夏地块之间的潜在边界应该在周潭集团当前位置的北部。