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Keywords:

  • crustal reworking;
  • Late Archean;
  • A-type granites;
  • adakite-like rocks;
  • anatexis;
  • North China Craton

In the Longwangzhuang area along the southern margin of the North China Craton (NCC), a layer of Cretaceous K-feldspar granites surrounds Paleoproterozoic granites. The Paleoproterozoic granites are enriched in sodic ferrogedrite and show low Al2O3 (12.3–13.0 wt%) and aluminum saturation index (ASI) (0.93–1.09) with high Zr (609–966 ppm), Y (47.2–96.7 ppm) and Nb (58.7–97.7 ppm) concentrations, resembling A-type granites. The Cretaceous K-feldspar granites have relatively high Sr (145–419 ppm), Ba (1252–1660 ppm), Sr/Y (19–127), La/Yb (36–56) ratios, but low Y (4.01–8.88 ppm) and Yb (0.46–0.99 ppm), geochemically resembling adakite-like rocks. However, these Cretaceous adakite-like K-feldspar granites have rather low MgO (0.08–0.26 wt%), Al2O3 (13.6–14.5 wt%), Mg# (11–23), Cr (2.30–4.61 ppm) and high initial 86Sr/87Sr (0.7098–0.7118), as well as abundant K-feldspar minerals, and are different from typical adakite. Zircon LA–ICP–MS geochronology shows that the two types of granites investigated in this study formed at 1616 ± 20 Ma and 140 ± 1 Ma, respectively. However, zircons from both the Paleoproterozoic and Cretaceous granites yield similar two-stage Hf model ages at ca. 2.5–2.6 Ga, suggesting the reworking of Late Archean juvenile crust. The Paleoproterozoic A-type granites show enriched Nd–Hf isotopic features but high whole-rock oxygen isotopes. These rocks may have formed from partial melting of restitic crustal material during lithospheric thinning, along with extension and experienced crystal fractionation of plagioclase, apatite and magnetite. The Cretaceous adakite-like K-feldspar granites were formed by local anatexis of TTG rocks from the Taihua Group, with amphibole as the major residual phase. The local anatexis and accompanying migmatisation suggest crustal compression and possible transpression. Therefore, the lithospheric thinning in the NCC should have taken place after 140 Ma on the southern margin of the NCC. Copyright © 2012 John Wiley & Sons, Ltd.