合肥盆地中部中—新生界沉积岩碎屑锆石
  <strong>LA-ICP-MS U-Pb</strong>定年及其地质意义

doi:10.11867/j.issn.1001-8166.2022.051

合肥盆地的形成演化与大别造山带具有密切的耦合关系，充填了来自造山带剥蚀的碎屑物质，从而记录了大别造山带隆升和剥蚀历史的关键信息。为了给大别造山带后碰撞阶段隆升演化历史提供信息，选择合肥盆地中部下白垩统朱巷组和古近系定远组开展详细的碎屑锆石LA-ICP-MS U-Pb定年工作。朱巷组碎屑锆石年龄特征相对复杂，主要表现为具有新元古代中期和三叠纪2个主年龄峰以及一系列次级年龄峰；定远组则主要具有新元古代中期主年龄峰，兼有部分古元古代和太古代末年龄峰。结合现有资料综合分析可知，朱巷组物源区主要为大别造山带，其下部地层向上部地层碎屑锆石年龄特征的转变反映了大别造山带后碰撞阶段造山带北部高压—超高压岩石逐渐被剥蚀殆尽的过程；定远组物源区主要为合肥盆地东侧的张八岭隆起，物源物质可能来源于该隆起内分布的震旦系。晚白垩世末—古近纪初，合肥盆地沉积岩的主要物源区由大别造山带转变为张八岭隆起。这为更好地认识合肥盆地及其周边地区的构造演化提供了新的证据。

关键词: 合肥盆地, 中—新生界地层, 碎屑锆石定年, 物源分析

Rock materials in an orogen are usually large-scale denuded and transferred to their surrounding basins during the post-collisional stage. Therefore, studies on sedimentary rocks in these basins are helpful for better understanding the evolutionary history of the orogen. The Hefei Basin, located north of the Dabie Orogen, was filled with clastic materials from the orogen, recording key information on its uplift and denudation history. In this study, sandstones of the Lower Cretaceous Zhuxiang Formation and siltstones of the Paleogene Dingyuan Formation in the central Hefei Basin were selected for detailed detrital zircon LA-ICP-MS U-Pb dating. The detrital zircon age frequencies in the Zhuxiang Formation show Triassic and middle Neoproterozoic age clusters, whereas the Dingyuan Formation has a predominant middle Neoproterozoic age cluster, with secondary age clusters in the Paleoproterozoic and the Archean. All the samples lacked or contained few Early Cretaceous zircon ages. Combined with the results of previous studies, it can be concluded that the provenance of the Zhuxiang Formation is mainly the Dabie Orogen and that its formation age corresponds to the late stage of the Fenghuangtai Formation in the southern Hefei Basin. Different detrital zircon age frequencies in different samples correspond to the process in which the high-pressure and ultrahigh-pressure rocks were gradually denuded in the Dabie Orogen during the Early Cretaceous. In the Paleogene, the Hefei Basin was surrounded by a series of uplifts, which greatly reduced the diversity of clastic material sources of the Paleogene Dingyuan Formation. Because the detrital zircon age frequencies of the Dingyuan Formation are consistent with those of the Sinian strata in the South China Block, it can be inferred that the source materials of the Dingyuan Formation mainly come from the Sinian of the Zhangbaling Uplift. The provenance of sedimentary rocks in the Hefei Basin changed from the Dabie Orogen to the Zhangbaling Uplift at the end of the Late Cretaceous or the beginning of the Paleogene.

Key words: Hefei Basin, Mesozoic-Cenozoic strata, Detrital zircon dating, Provenance analysis

中图分类号:

P597.3

图1 合肥盆地构造框架及沉积岩分布简图

Fig. 1 Simplified map for tectonic architecture of the Hefei Basin and distribution of sedimentary rocks

图2 合肥盆地中部沉积岩野外及显微照片
（a）朱巷组下部灰白色砂岩夹粉砂岩；（b）朱巷组上部紫红色泥质粉砂岩；（c）古近系定远组泥质粉砂岩；（d）朱巷组灰白色砂岩显微照片；（e）朱巷组紫红色粉砂岩显微照片；（f）定远组泥质粉砂岩显微照片

Fig. 2 Field photographs and photomicrographs of sedimentary rocks in the central Hefei Basin
（a） Gray white sandstone and siltstone in the lower part of the Zhuxiang Formation；（b） Purple red pelitic siltstone in the upper part of the Zhuxiang Formation；（c） Pelitic siltstone of the Paleogene Dingyuan Formation；（d） Micrograph of gray white sandstone of the Zhuxiang Formation；（e） Micrograph of purple red siltstone of the Zhuxiang Formation；（f） Micrograph of argillaceous siltstone of the Dingyuan Formation

图3 合肥盆地中部沉积岩部分锆石阴极发光图像

Fig. 3 Cathodoluminescence images of a selection of the dated zircons from the sedimentary rocks in the central Hefei Basin

图4 合肥盆地中部下白垩统朱巷组年龄频谱图及Th/U值

Fig. 4 Histograms and Th/U ratios of detrital zircons from the Lower Cretaceous Zhuxiang Formation in the central Hefei Basin

图5 合肥盆地中部古近系定远组年龄频谱图及Th/U值

Fig. 5 Histograms and Th/U ratios of detrital zircons from the Paleogene Dingyuan Formation in the central Hefei Basin

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摘要

LA-ICP-MS Detrital Zircon U-Pb Dating of Mesozoic-Cenozoic Sedimentary Rocks in the Central Hefei Basin and Its Geological Significance

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