Late Mesozoic Magmatic Intrusion Sequences Implication For The Transition Of Tectonic Regimes, Central Of The Dabie Orogenic Belt, China

The Dabie orogenic belt and the Su-lu region in central china are known to contain the largest distribution of ultrahigh pressure metamorphic rocks in the world, but also known to appear the strongest magmatism after ending of curst-crust collision. Abundant geochronology data show that the large-scale postcollisional magmatism is from 120 to 140 Ma in age. The main objects of this study are the late Mesozoic (Cretaceous) magmatic intrusions in the central of Dabie orogenic belt, aiming at the key scientific questions of the continental dynamics such as the relationship between the Mesozoic large-scale magmatism and the deep processes in East China. The purposes of this paper are: (1) to present intrusive sequences through field relationships, (2) to present new age information for magmatic intrusions using single zircon SHRIMP U-Pb dating, (3) to use geochemical and Sr-Nd isotope tracers associating with precise age data to constraint petrogenetic processes of these late Mesozoic rocks, and (4) to discuss geological evolution and continental dynamics processes for the Dabie collisional orogen in late Mesozoic.1. Field relationships. (1) The late Mesozoic magmatic intrusion sequences in the central of the Dabie orogenic belt from early to late are from mafic-ultramafic rocks, to gneissic quartz monzodiorite, which is found to be the earliest granodiorite in late Mesozoic by now, to porphyritic or augen monzogranites, which are the main body of the late Mesozoic huge magmatism in the Dabie orogenic belt, to fine monzogranites, to acidic (felsic) dykes including from K-feldspar pegmatite to alkali feldspar granite or granite-porphyry, and to dark dykes. The dark dykes are neutral dykes and basic dykes not to be distinguished in the field. (2) Mafic-ultramafic rocks are intimate intergrowth with gneissic quartz monzodiorite and porphyritic or augen monzogranites in the space. (3) The NE strike normal fault cut off acidic and basic dykes that implicate where there takes place a NW-SE brittle extensional tectonics after magmatism ending in the Dabie orogen. (4) The gneissic strike of Shigujian gneissic quartz monzodiorite is NE and NNE, which is consistent with ductile shear belt that parallel Tan-Lu fault. Tiantangzhai etc porphyritic or augen monzogranite have a local weekly gneissosity. It's obvious that there exist a tectonic event after emplacement of Shigujian pluton and before or at...