Geochronology and geochemistry of Late Mesozoic diabase in the Litun ore district, North China Craton

Abstract

Mesozoic mafic dykes in the Litun ore district provide an opportunity to study the nature of the Mesozoic lithospheric mantle beneath the Luxi area of the North China Craton. U–Pb dating of zircon from the Litun diabase using laser ablation inductively coupled plasma mass spectrometry yields an age of 124.6 ± 1.7 Ma, indicating an Early Cretaceous emplacement age. Samples from the Litun diabase display a medium‐ to fine‐grained texture, consisting of plagioclase (60–65 vol%), clinopyroxene (30–35 vol%), and minor biotite (~2 vol%). They are characterized by enrichment of large‐ion lithophile elements (LILEs, such as Rb, Ba, Th, and U) and light rare‐earth elements (LREEs) without significant Eu anomalies (0.83–1.07), depletion of high‐field‐strength elements (HFSEs, such as Nb, Ta, and Ti). The Litun diabase has relatively high initial 87Sr/86Sr ratios (0.7049–0.7060) and negative εNd(t) values (−11.7 to −9.7). The Litun diabase also shows high MgO (10.52–13.84 wt%), Cr (956–1,162 ppm), Co (26.5–65.6 ppm), and Ni (240–514 ppm) contents and low Rb/Sr ratios (0.01–0.03). These geochemical features suggest that the Litun diabase may have originated from an enriched lithospheric mantle source with amphibole as an essential phase, and that the Litun diabase was not significantly affected by fractional crystallization and crustal contamination. In combination with the Sr–Nd isotopic compositions of mafic rocks in the Luxi area (such as the Mengyin mafic dykes and Jinan gabbro), our results suggest that the lithospheric mantle beneath the Luxi area may have been rapidly enriched between ~144 and ~124 Ma, which was induced by sequential hybridization of sinked lower crust.