Prolonged Mantle Modification beneath the North China Craton: Evidence from Contrasting Mafic Dykes in Jiaodong Peninsula

The nature of lithosphere mantle beneath North China Craton (NCC) has been changed during the Mesozoic. We investigated the mafic dykes in Jiaodong to put constraint on the origin of them and reveal the mantle evolution of the NCC. Zircons from Kunyushan and Nansu mafic dykes give concordia U-Pb ages of 114.9 and 52.8 Ma, respectively. The Kunyushan mafic dyke has high MgO (similar to 8.0 wt.%) and Cr (>380 ppm) but lower FeO (<10 wt.%) contents. Large ion lithophile elements (LILE) are enriched compared to primitive mantle. The epsilon(Hf)(t) values of zircons are between -15.0 and -20.1. All these geochemical data imply an old and enriched lithosphere mantle source. In contrast, the Nansu mafic dyke has lower concentrations of MgO (<7.0 wt.%) and Cr (200 ppm-230 ppm) but higher FeO (>11 wt.%) contents. The LILE and light rare earth elements (LREE) are not so strongly enriched relative to the mafic dyke from Kunyushan but display slight enrichment compared to the primitive mantle. Positive zircon epsilon(Hf)(t) values are obtained (from +11.7 to +19.5, with one outlier of +3.4). It is suggested that the Nansu dyke sourced from an enriched MORB mantle and was generated by fluid flux melting.