Geochemical constraints of lamprophyres: Clues of Mesozoic tectonic interaction between the South China Block and North China Craton in Northern Jiangsu Province

Abstract

Early Cretaceous lamprophyre dykes widely occurred in the southeastern margin of the North China Craton (NCC), which are the important probes to understand the enrichment and depletion processes that modified the subcontinental lithospheric mantle of the NCC. In this research, one lamprophyre site (Liguo), which is the nearest lamprophyre to the South China Block (SCB) ever discovered in the NCC, had been used to analyze the influence of the deeply subducted SCB on the lithospheric evolution of the southeastern NCC. This lamprophyre was investigated by apatite U Pb dating with the age of 136 Ma, and it is depleted in HFSE, enriched in LILE and Sr–Nd–Pb isotope compositions ( 87 Sr/ 86 Sr (i) = 0.708038 to 0.709305, ε Nd (t) = −8.0 to −9.8, 206 Pb/ 204 Pb (t) ratios of 17.477 to 17.536, 207 Pb/ 204 Pb (t) of 15.548 to 15.552, and 208 Pb/ 204 Pb (t) of 37.944 to 38.004). Interpretations of minerals and whole rock elemental data suggest the Liguo lamprophyre was derived from 1 to 5% partial melting of garnet lherzolite; and MELTS modeling indicates fractional crystallization of ~26.5% clinopyroxene, ~0.1% spinel and ~ 3.5% garnet under 2.5 Gbar. Together with the Pb isotopic compositions of the contemporaneous lamprophyres in the Jiaodong Peninsula, it suggested that the mantle source of the Liguo lamprophyre was mainly modified by melts derived from partial melting of the subducted South China continental crust in the Triassic. In contrast, the magma sources for the lamprophyres in Jiaodong Peninsula were mainly modified by hydrous fluids derived from the subducted Paleo–Pacific oceanic crust in the Jurassic. Finally, it is concluded that the lithospheric mantle in the southeastern margin of the NCC is heterogeneous, and the subducted SCB could be the source of the enriched component in the southern margin of the NCC. • Liguo lamprophyre recorded the Mesozoic tectonic interaction between the SCB and NCC. • The lithospheric mantle in southeastern NCC is heterogeneous. • Subducted SCB is the source of the enriched component in the southern NCC.