The Early Carboniferous Xiaomiaogou granite porphyry dykes in the northern margin of the North China Craton: implication for crust–mantle interaction and intraplate magmatism

The age, petrogenesis and geodynamic implication of Xiaomiaogou granite porphyry dykes in the northern margin of the North China Craton were investigated using geochronology, geochemistry and Sr-Nd-Pb-Hf isotopic data. LA-MC-ICP-MS zircon U-Pb dating yielded the concordant Pb-206/U-238 weighted mean age of 350.4 +/- 1.4 Ma for the dykes, suggesting they were the productions of the Early Carboniferous magmatism in the northern margin of the North China Craton. The granite porphyries display the pronounced A-type affinities: apart from higher zircon saturation temperature, they are high-K calc-alkaline and metaluminous, with high concentrations of K2O+Na2O varying from 7.93 to 8.55wt.%, incompatible elements (e.g. Zr, Y, Nb and Ce), REEs and 10000Ga/Al ratios but less obvious LREE and HREE fractionation. With the lower initial Sr-87/Sr-86 ratios (0.7055 to 0.7070), negative values of epsilon(Nd)(t) (-7.1 to -4.9) and epsilon(Hf)(t) (-11.2 to -8.0) and old Nd (1505 to 1681 Ma) and Hf (1861 to 2061 Ma) model ages, all the rocks exhibit the similar geochemical compositions to the melts obtained in experimental studies by dehydration melting of meta-basalts, implying a lower continental crust origin. However, the high Mg-# values (47.53 to 53.60) and subcontinental lithospheric mantle-like epsilon(Nd)(t), epsilon(Hf)(t) and Pb isotopic compositions ((Pb-206/Pb-204)i = 17.296-17.766, (Pb-207/Pb-204)i = 15.460-15.490 and (Pb-208/Pb-204)i = 37.097-37.568) indicate the involvement of melts from subcontinental lithospheric mantle. Combined with the special features of mafic microgranular enclaves occurring within the granite porphyries, mixing of the lower crust and subcontinental lithospheric mantle of the North China Craton is proposed for the genesis of granite porphyry dykes in this study. During the hybrid magma ascending, pronounced fractional crystallization and crustal assimilation may have also occurred. Based on geochemical criteria, the Xiaomiaogou granite porphyries can be classified into A(1) group. Characterized by the compositional features of anorogenic granites, an intraplate setting is envisaged for the formation of Xiaomiaogou granite porphyry dykes. Such a tectonic environment may be related to the northward drift of the North China Craton during rifting away from East Gondwana. Copyright (C) 2016 John Wiley & Sons, Ltd.