| 华北克拉通东南部淮南地区晚前寒武纪寿县组碎屑岩粒度特征及锆石U-Pb年代学分析 |
| 投稿时间：2024-09-30 修订日期：2025-01-13 点此下载全文 |
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| 基金项目:由国家自然科学基金项目(编号: 41902212)、矿山地质灾害防治安徽省重点实验室开放基金课题(编号: 2023-MGDP-06)和安徽省科技厅重点研发项目(编号: ZMXJ-LZ-JS-2020-16)联合资助。 |
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| 中文摘要:寿县组是华北克拉通东南部广泛发育的一套前寒武纪碎屑岩地层, 长期来对其沉积时限的认识有较大分歧。由于寿县组上、下相邻层位中均产有丰富宏体藻类化石, 因而查明其岩性特征、沉积环境、沉积时限以及沉积物源等方面内容对认识晚前寒武纪古地理变迁、生物地层层序对比以及沉积大地构造演化均具有重要意义。本研究选择该套层序中的寿县组为研究对象, 通过野外调查确定淮南地区寿县组的出露位置、岩性和层序特征, 采集5处岩石样品进行显微镜下观察和粒度分析, 并开展了LA-ICP-MS碎屑锆石U-Pb年龄测定, 以分析寿县组的沉积环境、沉积时限以及沉积物源特征。研究表明, 寿县组是一套中-厚层钙质细碎屑岩, 偶夹中-薄层泥质岩沉积序列, 粒度分析结果显示其沉积粒度属于细砂岩与粗粉砂岩过渡类型, 粒度组成中以悬浮搬运组分为主, 跳跃搬运组分较少, 成熟度较高, 沉积水动力条件较弱, 结合海绿石矿物的出现以及萨胡判别函数计算结果推断处于临滨带和过渡带之间的陆棚环境。5个样品中最年轻的单颗粒碎屑锆石年龄分别为962±25、963±31、954±25、952±24和976±26 Ma。淮南地区寿县组全部碎屑锆石年龄中最年轻一组的加权平均年龄为953±9 Ma, 结合徐州-淮北地区侵入至相当层序中的基性岩床群943~876 Ma的侵入年龄, 将寿县组沉积时间限定在953~943 Ma。淮南地区寿县组碎屑锆石年龄频谱具有1.8 Ga以来的年龄数量逐步增多, 并且富含1.2~1.0 Ga年龄的规律, 综合分析认为寿县组主要的沉积物源应来自于华北克拉通之外曾经相连的陆块或陆块群, 但不能排除华北克拉通内部可作为次要的物源区。 |
| 中文关键词:寿县组 粒度分析 碎屑锆石U-Pb定年 最大沉积时间 沉积物源 |
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| Grain size characteristics and zircon U-Pb geochronological analysis on the precambrian clastic rocks of the Shouxian Formation in the Huainan region, southeastern North China Craton |
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| Abstract:The Shouxian Formation is a set of Precambrian clastic strata widely developed in the southeast part of the North China Craton, and the understanding of its deposition time has been divergent for a long time. Since there are abundant macroalgae fossils in the upper and lower adjacent strata of Shouxian Formation, it is of great significance to identify the lithology, sedimentary environment, timing and sources for understanding the late Precambrian paleogeography, biostratigraphic sequence correlation and sedimentary tectonic evolution. In this study, the outcrop locations, lithologies and sequence characteristics of the Shouxian Formation from such late Precambrian successions in the Huainan area were determined through detailed field investigation. Five rock samples were collected for microscopic observation, grain size analysis, and LA-ICP-MS detrital zircon U-Pb dating, in order to analyze the depositional environment, time constraints and sediment source characteristics of the Shouxian Formation. The study indicates that the Shouxian Formation is a set of medium to thick-bedded calcareous fine clastic rocks, occasionally interbedded with medium to thin-bedded muddy layers. The grain size analysis results show that it belongs to the transitional type between fine sandstone and coarse siltstone, and the grain size composition is dominated by suspended load components, less saltation load components, with high maturity and weak depositional hydrodynamic conditions. Combined with the appearance of glauconite minerals and the calculation results of Sahu discrimination function, it is inferred that the sedimentation is in a shelf environment between the littoral zone and the transitional zone. The youngest single-grain detrital zircon ages of the five samples are 962±25, 963±31, 954±25, 952±24, and 976±26 Ma, respectively. The weighted average age of the youngest set of detrital zircon ages from the whole samples of Shouxian Formation within the Huainan area is 953±9 Ma. Combined with the intrusive age of the mafic sill complexes of 943 to 876 Ma in the Xuzhou-Huaibei area, which intrudes into the equivalent stratigraphic sequence, the depositional time of the Shouxian Formation is constrained to be between 953 and 943 Ma. The detrital zircon age spectrum of the Shouxian Formation shows a gradual increase in the number of detrital zircons since 1.8 Ga, and it is rich in detrital zircons of 1.2 to 1.0 Ga. A comprehensive analysis suggests that the main sediment source of the Shouxian Formation should come from a landmass or landmass groups that were once connected outside the North China Craton, but it cannot be ruled out that the interior of the North China Craton could also serve as a secondary source area. |
| keywords:Shouxian Formation grain size analysis detrital zircon U-Pb dating maximum depositional age sediment provenance |
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