Abstract

We investigated the spatial-temporal distribution and the major, trace, and rare earth element geochemistry, U-Pb zircon geochronology, and isotope geochemistry of mafic dike intrusions in the Jiadong Peninsula (NE China). The newly obtained zircon dates tightly constrain the timing of dike emplacement to 130–110 Ma, following an earlier episode (155–144 Ma) of magmatism in the eastern part of the North China craton. This Cretaceous magmatism was associated with large-scale lithospheric extension in the North China craton, and hence its petrogenetic and geochemical evolution provides significant insights for the nature of melt evolution during this cratonic thinning event. The majority of the Early Cretaceous dikes intruding the crystalline basement rocks within the Jiaobei terrane and the Sulu orogenic belt in the Jiadong Peninsula display large ion lithophile element (LILE) enrichment, high field strength element (HFSE) depletion, and enriched Sr-Nd isotopic values, indicating arc-like geochemical signatures. These features collectively point to derivation of dike magmas from partial melting of a subduction-metasomatized lithospheric mantle. High Dy/Yb ratios of dike rocks between 2.09 and 2.63, with an average value of 2.31, suggest that their magmas originated from low-degree partial melting of an amphibole-bearing lherzolitic mantle lithosphere in the garnet-spinel transition zone. The low platinum group element (PGE) compositions of the dike rocks further indicate that their magmas were produced from S-saturated melts, derived from low-degree partial melting of the inferred mantle source. These S-saturated melts did not undergo significant sulfide segregation and crustal contamination, but they did experience early fractionation of laurite and Os-Ir-Ru alloys. The minor occurrence in the Jiadong Peninsula of ca. 121 Ma mafic dikes with oceanic island basalt–like geochemical fingerprints also indicates an asthenospheric melt contribution into the Early Cretaceous magmatism across the North China craton. We infer that the emplacement of the Mesozoic (Late Jurassic–Early Cretaceous) mafic intrusions in the Jiadong Peninsula was a magmatic response to cratonic thinning, caused by slab rollback–induced delamination of the lithospheric mantle of the North China craton, and that this mafic magmatism migrated eastward in time and space during the Cretaceous.

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