中国地质调查局项目(DD20230209, DD20221649, DD20190003); 国家自然科学基金(42372237, 41772191, 41572175, 41972205, 41172171)
从滹沱群底部四集庄组不同的分布区选择了1件正长花岗斑岩、1件似斑状二长花岗岩砾石及1件侵入于蒋村四集庄组的正长花岗斑岩,进行了锆石U-Pb-Hf同位素分析。获得正长花岗斑岩和似斑状二长花岗岩砾石的锆石207Pb/206Pb加权平均年龄分别为2 507±14 Ma和2 519±35 Ma,推断花岗岩砾石的物源可能为五台新太古代晚期峨口花岗岩和兰芝山花岗岩;侵入于四集庄组的正长花岗斑岩锆石207Pb/206Pb年龄为2 157±15 Ma。结合四集庄组、五台地区高凡群火山岩年龄结果和华北克拉通2.2~2.0 Ga地质事件的性质,认为滹沱群底界可能为2.2~2.18 Ga,顶界时代约为2.0 Ga,其沉积对应一期强烈的陆内裂谷伸展过程。新太古代花岗岩砾石和古元古代花岗岩锆石Hf同位素结果指示,五台地区新太古代早期出现明显的地壳生长,新太古代晚期也存在地壳增长。
From the different distribution areas of the Sijizhuang Formation at the bottom of the Hutuo Group, one sample of orthoclase granite-porphyry and one sample of porphyritic monzogranite gravels were selected, along with one sample of orthoclase granite-porphyry intruded into the Sijizhuang Formation in Jiangcun area. Zircon U-Pb-Hf isotope analysis was conducted. The weighted average ages of the orthoclase granite-porphyry and the porphyritic monzogranite gravel were determined to be 2 507±14 Ma and 2 519±35 Ma, respectively, indicating that the sources of the granite gravels were likely the late Neoarchean Ekou granite and Lanzhishan granite. The zircon 207Pb/206Pb age of the orthoclase granite-porphyry intruded into the Sijizhuang Formation was determined to be 2 157±15 Ma. Combining the ages of the Sijizhuang Formation and the Gaofan Group volcanic rocks in the Wutai area, and the geological events in the North China Craton from 2.2 to 2.0 Ga, it is inferred that the lower boundary of the Hutuo Group is likely to be 2.2 to 2.18 Ga, and its upper boundary age is approximately 2.0 Ga. The depo- sition process represents a period of intense intracontinental rift setting. The Hf isotope results of the Neoarchean granite gravel and the Paleoproterozoic granite zircons indicate that there was strong crustal growth in the early Neoarchean and crustal growth also existed in the late Neoarchean in the Wutai area.