Acta Petrologica et Mineralogica

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.

Wutai area; the Hutuo Group; the Sijizhuang Formation; zircon U-Pb-Hf isotope; sedimentation time range