Water Contents of Early Cretaceous Mafic Dikes in the Jiaodong Peninsula, Eastern North China Craton: Insights into an Enriched Lithospheric Mantle Source Metasomatized by Paleo–Pacific Plate Subduction–Related Fluids Available to Purchase

The Early Cretaceous lithospheric mantle beneath the Jiaodong Peninsula has been recognized as ancient and enriched mantle with widespread mafic dike swarms. However, the enriching agent and the process of the lithospheric mantle remain under debate. In this study, we recovered the H₂O contents of the primitive magmas of Early Cretaceous mafic dikes in the Jiaodong Peninsula by using the H₂O contents of clinopyroxene (Cpx) phenocrysts and H₂O partition coefficients $DH2Ocpx/melt$⁠. We also present whole-rock geochemical data and in situ major- and trace-element contents for Cpx phenocrysts from these mafic dikes. These dikes are characterized by low SiO₂ contents, high MgO contents, enrichment of large-ion lithophile elements and light rare earth elements, depletion of high-field-strength elements, high (⁸⁷Sr/⁸⁶Sr)_i ratios, and low ε_Nd(t) values. These geochemical features imply an origin of enriched subcontinental lithospheric mantle. The calculated H₂O contents of the primitive magmas range from 1.38 to 4.45 wt%, with associated H₂O/Ce ratios varying from 237 to 322, suggesting that their mantle source was metasomatized by oceanic slab subduction–related fluids. In addition, covariations between H₂O/Ce and incompatible elements indicate the addition of a dehydrated marine sediment component in the mantle source of the Jiaodong mafic dikes. In combination with the H₂O contents of Early Cretaceous basaltic rocks in the southeastern North China Craton, the lithospheric mantle was metasomatized through fluids related to paleo–Pacific plate subduction.