Late Archean crustal growth in the North China Craton and its link to the gradual evolution of plate tectonics

A wealth of geological and geochemical evidence indicates that plate tectonics was initiated in the Archean, though its style differing from that in the Phanerozoic, largely due to higher temperatures of convective mantle. Understanding the specific characteristics for the operation of ancient plate tectonics is critical for deciphering the formation and evolution of continental crust on early Earth, as well as the progressive development of Earth’s habitability. Through an in-depth analysis of geology and geochemistry for two events of late Archean crustal growth in the North China Craton, this study suggests that Archean plate tectonics would likely undergo the gradual evolution from immature to mature phases. The North China Craton experienced two major episodes of crustal growth at ~2.9–2.7 and ~2.6–2.5 Ga, respectively, represented by peaks in isotopic model ages of Archean felsic gneisses and widespread mafic rocks in greenstone belts. Although the preserved mafic rocks in greenstone belts generally exhibit arc-like trace element signatures, the early mafic crust formed at ~2.9–2.7 Ga is limited in volume, with most of it having been reworked within several hundred million years. Tonalite-trondhjemite-granodiorite (TTG), produced by partial melting of such mafic crust, show zircon Hf-O isotope compositions indicative of sources consisting of seawater-hydrothermally altered oceanic crustal rocks with varying ages, suggesting that the early mafic crust was likely dominated by oceanic basalts. The medium- to low-pressure signatures of TTG rocks further imply that the oceanic crust was not subducted deeply to mantle depths, but instead was accreted to the margin of proto-continental nuclei due to aborted subduction. In contrast, the ~2.6–2.5 Ga crustal growth event preserved a greater volume of mafic rocks. For these mafic rocks, the enrichment of incompatible elements correlates with water contents estimated from whole-rock major elements, indicating that their arc-like trace element features were associated with fluid metasomatism of the source region. Integrated with regional geological evidence from ~2.5 Ga, such as ophiolites containing ultrahigh-pressure mineral inclusions and eclogite-facies remnants of oceanic crust, these observations suggest that modern-style plate subduction was likely in operation by the end of the Late Archean. Therefore, the modern plate tectonics regime did not emerge abruptly, but underwent a gradual evolution controlled by the thermal state of plate margins. It is this evolving tectonic regime that drove the significant crustal growth during the Archean. The two distinct episodes of crustal growth ultimately led to the formation of the North China Craton.