Investigating late Mesoarchean crustal dynamics in the North China Craton through 2.84 Ga TTG gneisses of the Xiong'ershan area

Abstract

The late Mesoarchean era was a critical period for the Earth's geodynamic regime. However, it remains unclear which geodynamic regime dominated this stage and how different geodynamic regimes transitioned or interacted with each other. From the perspective of crust-mantle interactions, effectively identifying different geodynamic regimes and establishing corresponding geochemical indicators are key to addressing these scientific questions. The Mesoarchean era is highlighted as a key phase in the initial formation of Earth's crust. This research delves into the late Mesoarchean TTG rock suite located in the Xiong'ershan region to shed light on the crustal dynamics of the Mesoarchean era within the North China Craton (NCC). These rocks exhibit zircon U-Pb ages of 2836 ± 26 Ma and display characteristics such as Mg^# (48–66), negative Eu anomalies (0.68–0.83), and relatively low Sr/Y (23.01–47.26) and (La/Yb)_N (5.24–39.85) ratios. Zircon grains from these rocks reveal ε_Hf(t) values spanning 0.3 to 3.6, reflecting Hf model ages between 2963 and 3087 Ma. ε_Nd(t) values of 3.23 with Nd model ages for the whole rock mass peak at 2872 Ma, indicating the formation of juvenile crust during this era. Zircon δ¹⁸O isotopic values (4.73–6.29 ‰, with an average of 5.32 ‰) suggest a mantle-derived origin for the magma. Magma crystallization temperatures, estimated using zircon Ti-thermometry, were between 607 and 725 °C. The TTG gneisses show moderate Ce/Sr ratios (0.06–0.26) and Y content (7.1–23.8 ppm), consistent with medium-pressure formation conditions. The observed depletion in HFSE (e.g. Nb, Ta, Zr, Hf, average value is 149.6) and HREE (6.22–14.99) alongside enrichment in LILE (e.g. Rb, Sr, Ba, average value is 993.9) and LREE (53–156) in these late Mesoarchean TTG rocks from the Taihua complex suggest that they formed in an arc magmatism setting related to subduction. These findings are critical for understanding the early growth and development of the NCC's crust and affirm the theory that global subduction tectonics began around 2.8 Ga.