Zircon U-Pb age, geochemical, and Sr-Nd-Hf isotopic constraints on the origin of Early Cretaceous mafic dykes from western Shandong Province, eastern North China Craton, China

Mesozoic mafic doleritic dykes form swarms that are widespread across Shandong Province in the eastern North China Craton (NCC). We present U-Pb zircon ages, geochemical data, and Sr-Nd-Hf isotopic data for representative samples of these dykes. U-Pb zircon analyses for four samples, using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), yielded ages that range from 121.9 +/- 0.6 to 124.3 +/- 0.5 Ma (Early Cretaceous time). The dolerites are characterised by a narrow range of rock compositions. They display enrichments in light rare earth elements and large ion lithophile elements (i.e., Rb, Ba, U, K and Pb), as well as depletion in high field strength elements (Nb, Ta and Ti). The mafic dykes have uniform (Sr-87/Sr-86), values of similar to 0.7098, low epsilon(Nd)(t) values in the range of -14.7 to -14.5, epsilon(Hf)(t) values (for zircon) are between -31.4 and -26.7 and high hafnium model ages (t(DMI) = 1817 similar to 2024 Ma). These results indicate that the mafic dykes were derived from partial melting of an enriched, lithospheric mantle source. The magmas underwent direct crustal contamination. In summary, the origin of the dykes can be attributed to the collision between the NCC and the Yangtze Craton, the magmas that formed these dykes were sourced from a hybridized source caused by subduction of Yangtze crustal sedimentary material beneath southeastern before the Late Mesozoic.