Abstract:

The early Precambrian crustal growth models and related crustmantle geodynamics have always been the research focus of international Precambrian community. Although it is generally accepted that the continental crust was dominantly formed during the Archean period, the definite crustal growth models and crustmantle geodynamic regimes remain largely controversial. Some researchers advocate the vertical tectonic regimes, e.g., plume or lower crust delamination models, whereas others favor the lateral subductionaccretion processes or plumearc interaction models. Recent studies reveal that several essential changes occurred during the late Archean crustal evolution history of the earth, i.e., rapid decrease in the ratio of komatiites within metavolcanic sequences; the wide emplacement of potassiumrich granitoid gneisses; and the apparent increase of the crustal recycling processes. All the above lines of evidence indicate that the crustmantle geodynamic regimes may have significantly changed during the late Archean. The North China Craton (NCC) is characterized by intense ~2.52.6 Ga tectonothermal events, which offers valuable opportunities for us to investigate the transitional regimes of early Precambrian crustmantle geodynamic evolution. In this study, we provide a timely review of recent early Precambrian studies along the northwestern margin of the Eastern Block (EB), especially focusing on the petrogenesis and crustmantle interaction processes recorded by the late Neoarchean (~2.52.6 Ga) metavolcanic rocks in the Western and Northern Liaoning Provinces, Eastern Hebei Province, and the Wutai granitegreenstone belt. It is suggested that the metamorphosed mafic rocks in these areas can be subdivided into three petrogenetic types of MORB (Midocean ridge basalt)type, IAT (Island arc tholeiite)type and the CAB (calcalkaline basalt)type. These Neoarchean metavolcanic rocks are considered to be formed by the partial melting of the asthenospheric mantle underneath an Archean spreading ridge and of the mantle wedge peridotites variably metasomatized by slabderived fluids, respectively. On the other hand, the metamorphosed andesitic to dacitic rocks may be generated by the partial melting of the subducted oceanic slabs and the interactions between melts from the slab and mantle wedge materials, showing analogous to either high magnesian andesites (HMAs) or Phanerozoic adakites. Integrated with recent early Precambrian studies of entire EB, we propose that the NCC has experienced intense crustal growth during the late Archean period (~2.5 and ~2.7 Ga), of which, the early Neoarchean episode (~2.7 Ga) of crustal growth is controlled by the plumearc interaction processes, whereas the late Neoarchean episode (~2.52.6 Ga) is dominated by the lateral subductionrelated intraoceanic arc and arccontinent accretion processes. Similar late Neoarchean tectonothermal events related to lateral subductionaccretion processes have been widely reported from the Tarim Craton, southern India, Vestfold Hills terrane of East Antarctica, and the Gawler Craton of Australia, and they may represent the key geological responses to the arrival of Phanerozoiclike plate tectonic regimes and the first global supercontinent (i.e., Kenorland) during the terminal Archean.

Key words: Early Precambrian crustal growth, crustmantle geodynamic regimes, North China Craton, supracrustal metavolcanic rocks, Late Archean arccontinent accretion