Two stages of the early Cretaceous post-orogenic granitoids are identified in the Dabie orogen, eastern China, which recorded processes of the extensional collapse of the orogen. The early stage (approximate to 132Ma) granitoids consists of hornblende quartz monzonites and porphyritic monzogranites, they are pervasively deformed and have high-K adakitic geochemical characteristics. Their eochemical features indicate that they were formed by partial melting of over-thickened (> 50km) lower continental crust. The late stage (approximate to 128Ma) undeformed granites consists of fine-grained monzogranites, fine-grained K-feldspar granites and coarse-grained K-feldspar granite-porphyry, which have no adakitic geochemical signatures. Their eochemical features indicate that they were produced by partial melting of the lower continental crust that already uplifted into much shallower levels (< 35 km). The initial Sr-87/Sr-86 ratios and epsilon(Nd) (t) values of the early stage foliated hornblende quartz monzonites range between 0.7066 similar to 0.7076 and - 20.3 similar to - 27.8, respectively, resembling that of the mafic granulites of the Yangtze lower continental crust. The cretaceous zircons have very negative initial Hf isotope compositions (epsilon(Hf) (t) = - 29.3 +/- 0.5) and very old two-stage Hf model ages (t(DM2) = 3030 =/- 65 Ma). We suggest that the foliated hornblende quartz monzonites were derived from partial melting of the mafic lower continental crust with about 3.0 Ga zircon Hf model ages. The initial Sr-87/Sr-86 ratios and epsilon(Nd) (t) values of the early stage foliated porphyritic monzogranites range between 0.7078 similar to 0.7083 and - 15.8 similar to -20.0, respectively, resembling those of the tonalitic to granitic gneisses in the North Dabie. Their Cretaceous zircons also have negative epsilon(Hf) (t) Values of - 24.8 +/- 0.5 and old t(DM2) of 2744 +- 34Ma. We regard that the foliated porphyritic monzogranites were derived from the partial melting of the felsic lower continental crust with about 2.7Ga zircon Hf model ages. These features suggest that the over-thickened lower continental crust under the Dabie orogen before the Cretaceous collapse are double-layerd: a 3.0Ga (zircon Hf model ages) mafic lower-most crust and a 2.7Ga felsic (tonalitic to granitic) upper lower crust. The initial Sr-87/(86) Sr ratios and epsilon(Nd) (t) values of the late stage undeformed granites range between 0.7069 similar to 0.7105 and - 16.4 similar to -22.1, respectively, which are also resemble those of the tonalitic to granitic gneisses in the North Dabie. Their Cretaceous zircons have a wide range of epsilon(Hf) (t) values (- 25.2 similar to 7.4). Most of their Cretaceous zircon grains gave negative epsilon(Hf) (t), which yields two peak of - 22.5 +/- 0.5 and - 16.3 +/- 0.7; correspondingly, their zirocn t(DM2) are 2600 +/- 40Ma and 2211 +/- 68 Ma respectively. A few Cretaceous zircons give positive epsilon(Hf) (t) values of 5.8 similar to 7.4, their zirocn t(DM2) are 743 +/- 130Ma. We suggest that the late stage undeformed granites were derived from the partial melting of the felsic lower continental crust with about 2.6 similar to 2.2Ga zircon Hf model ages. The occurrence of Cretaceous zircons which have positive epsilon(Hf) (t) values (5.8 similar to 7. 4) and Neoproterozoic t(DM2) ages (743130Ma) indicate the presence of juvenile crust in their source, which might have formed by input of anseosphere- derived magma during the break-up of Rodinia supercontinent in Neoproterozoic. These features indicate that the collapsed lower continental crust was mainly composed of 2.6 similar to 2.2Ga felsic (tonalitic to granitic) basement coupled with rare juvenile crust formed during the break-up of Rodinia supercontinent in Neoproterozoic.
