Neoarchean continental crust evolution of the southern North China Craton: constrains from geochronology and geochemistry of the Dengfeng complex in the Jishan area

A whole-rock geochemical and zircon U-Pb and Lu-Hf isotope study of the Dengfeng complex in the Jishan area was performed to constrain the Neoarchean continental crust evolution in the southern margin of the North China Craton (NCC). The Dengfeng complex can be divided into supracrustal assemblage and plutonic intrusion. In the supracrustal assemblage, the detrital zircon of quartz schist from the Guojiayao Formation display oscillatory growth zones and streaky absorption with relatively high Th/U ratios (0.36-2.10), suggesting a magmatic origin. The Pb-207/Pb-206 ages range from 2963 to 2531 Ma, with a peak age of 2555 Ma, and the epsilon(Hf)(t) values are between + 2.3 and + 12.1. Combined with previous studies, the depositional age of the Guojiayao Formation can be constrained between 2542 and 2522 Ma, indicating that it mainly originated from the Neoarchean accretive basement material of the southern NCC. The Ruzhou gneissic syenogranites yield U-Pb ages from 2515 +/- 13 Ma to 2504 +/- 20 Ma, show that the plutonic intrusions also formed in the Late Neoarchean. They have high SiO2 (64.03-73.99 wt%) and Na2O + K2O (8.79-14.58 wt%) contents but low MgO (0.19-0.36 wt%) and CaO (0.02-0.27 wt%) contents, and belong to slightly peraluminous I-type granites with shoshonitic affinity. Magmatic zircon grains have positive epsilon(Hf)(t) values (+ 0.2 to + 6.7) with average crustal Hf model ages ranging from 2911 to 2671 Ma (average of 2765 Ma), indicating that the Ruzhou gneissic syenogranites were likely produced by partial melting of the accretive lower crust. The positive epsilon(Hf)(t) values and similarly ancient model ages suggest that a large-scale continental crust growth occurred in the southern margin of NCC at ca. 2.7 Ga. The Dengfeng complex was mainly derived from an arc-related setting associated with subduction in the Late Neoarchean.

Automated summary

A study of the Dengfeng complex in the Jishan area reveals the evolution of the Neoarchean continental crust in the southern margin of the North China Craton. The results show that the supracrustal assemblage in the Dengfeng complex mainly originated from the accretive basement material of the southern NCC, while the plutonic intrusions formed in the Late Neoarchean through partial melting of the accretive lower crust. The study also suggests a large-scale continental crust growth in the southern margin of NCC at around 2.7 Ga.