Formation of Wulong Mafic Dikes via Mixing of Enriched Lithospheric Mantle-Derived and Crustal Magmas, Eastern North China Craton

Abstract

Zircon U-Pb age and geochemical data are reported for the Wulong dike swarms from the Liaodong Peninsula, NE China. The studied dikes include diorite, lamprophyre, and dolerite. Together with previous dating, the diverse rocks have a peak age of ca. 120–125 Ma. They are marked by inversely zoned phenocrysts with Mg- and Cr-rich rims, and they exhibit mantle-like signatures (i.e., high Mg-Cr-Ni) associated with prominent subduction-type element enrichments. The early diorites have relatively radiogenic Sr (–0.7143) and less radiogenic Nd ( to −11.0) isotopes coupled with high and variable MgO (Cr, Ni) contents, indicating that they were mainly derived from ancient lower crust with subordinate contributions of enriched lithospheric mantle. The transitional lamprophyres are characterized by high Rb/Sr ratios (0.22–0.54) but low initial 87Sr/86Sr ratios (0.7069–0.7093), moderate negative εNd(t) values (−14.4 to −12.6), and low promantle elements (such as Mg-Cr-Ni), reflecting that juvenile lower crustal components with a short residence time were significantly added to their source as well. The late dolerites possess extremely high Mg, Cr, and Ni concentrations, less radiogenic Sr (–0.7082) and much radiogenic Nd ( to −2.4) isotopes, suggesting that they mainly originated from an enriched mantle source with minor involvement of old lower crustal materials. Petrographic and chemical evidence points to an origin of these rocks by mixing of enriched mantle-derived and lower crustal magmas. The rapid progressive change of source compositions first indicates a complex, multistage hybridization process, and second, it shows an extensional tectonic regime during magma generation.