Early Cretaceous low-Mg adakitic granites from the Dabie orogen, eastern China: Petrogenesis and implications for destruction of the over-thickened lower continental crust

摘要: It is generally accepted that the low-Mg adakitic rocks were derived from partial melting of metabasalts/eclogites. In this study, we demonstrate early Cretaceous granites in North Dabie Complex (NDC) generated by NDC orthogneisses. Here present in-situ U–Pb and Lu–Hf isotopes zircon with whole-rock geochemical Sr–Nd isotopic compositions carried out for Tiantangzhai porphyritic monzogranites orogen, eastern China. The are characterized high Sr (576–988 ppm), low Y (7.3–19.0 ppm), depletion HREE (Yb: 0.50–1.78 ppm) (thus resulting Sr/Y (34.3–135.2) (La/Yb)N (17.0–105.2) ratios) without a negative Eu anomaly. They also exhibit SiO2 (66.5–73.5 wt.%) K2O (2.7–4.7 wt.%), MgO (0.4–1.6 wt.%) or Mg# (28.2–45.3, mostly < 40) values. Whole-rock suggest represent rock high-Si rich-K features equilibrated residues rich garnet. (eNd (t) = − 16.2 to − 20.3, (87Sr/86Sr)i = 0.707798–0.708804, tDM2(Nd) = 2.3–2.6 Ga) distinct eclogites amphibolites but similar Neoproterozoic (700–800 Ma) gneisses NDC. dating zircons gives consistent age 130.0 ± 3.4 Ma discordia upper intercept 716 ± 34 Ma inherited cores identified CL imaging. Correspondingly, analyses young age-spots yield initial 176Hf/177Hf ratios 0.281898 0.282361, eHf(t) values − 28.1 − 17.6 two-stage “crust” Hf model ages (tDM2) 2293 ± 89 2949 ± 108 Ma, which agreement 0.281891 0.282218, − 28.2 − 11.7 1927 ± 87 2963 ± 92 Ma pre-Mesozoic cores, respectively. As individual core-rim pairs zircon, Th/U increase growth rims possibly due variable degrees melting, whereas 176Lu/177Hf greatly decrease because garnet effect residues. Thus, gneisses, foundering garnet-bearing could have caused destruction over-thickened lower continental crust.