Neoarchean subduction to back-arc extension in the North China Craton: Insights from the Dengfeng basic rock

Abstract

The scarcity of the early Precambrian geological record limits our comprehension of crucial information concerning interactions between the crust and mantle, mechanisms involved in subduction zone arc-continental collisions, as well as patterns of mantle enrichment and crustal growth during this epoch. The Dengfeng terrane in the North China Craton provides significant data on Precambrian crustal evolution, particularly within the Neoarchean magmatic suites. Our study focuses on a variety of basic rocks across several locations in this region. Basic rocks from Huishansi and Sanhuangzhai (2558–2525 Ma) exhibit characteristics such as low SiO₂ (45.44–56.54 wt%), K₂O (0.77–2.7 wt%), Na₂O (1.66–4.51 wt%), and high MgO (4.66–11.22 wt%) and FeO_T (8.17–13.77 wt%). Similarly, basic rocks from Shipaihe and Guojiayao (2480 Ma) also display low SiO₂ (46.16–52.48 wt%), K₂O (0.24–1.28 wt%), and Na₂O (1.87–3.75 wt%), with FeO_T (1.07–2.31 wt%), but feature higher content of MgO (5.33–8.83 wt%) and Mg^# (44–62, averaging 53). Both sets exhibit relatively flat REE patterns and weak negative anomalies in Nb, Ta, and Ti, corresponding to a tholeiitic basalt composition for the protoliths. Analyzing low (Hf/Sm)_N, (Nb/La)_N, and Th/Yb ratios, coupled with depleted HFSE, suggests potential crustal contamination in the rocks from Huishansi and Sanhuangzhai. Further, based on low V/Sc ratios (5.38–10.27, average 7.02) and depleted zircon Ɛ_Hf(t) values, our proposition is that the magma was sourced through partial melting of a depleted and relatively reduced mantle source. These findings offer valuable insights into the tectonic evolution of the Dengfeng terrane, spanning from subduction to post-collisional extension.