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.

中文翻译：

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华北克拉通里屯矿区晚中生代辉绿岩年代学和地球化学

里屯矿区的中生代基性岩脉为研究华北克拉通鲁西地区下中生代岩石圈地幔的性质提供了机会。使用激光烧蚀电感耦合等离子体质谱法对里屯辉绿岩中的锆石进行 U-Pb 定年，得出年龄为 124.6 ± 1.7 Ma，表明早白垩世就位年龄。来自里屯辉绿岩的样品显示出中至细粒纹理，由斜长石（60-65 vol%）、斜辉石（30-35 vol%）和少量黑云母（~2 vol%）组成。它们的特点是富集大离子亲石元素（LILEs，如 Rb、Ba、Th 和 U）和轻稀土元素（LREEs），没有明显的 Eu 异常（0.83-1.07），耗尽高场-强度元素（HFSE，例如 Nb、Ta 和 Ti）。里屯辉绿岩具有较高的初始⁸⁷ Sr/ ⁸⁶ Sr 比率 (0.7049–0.7060) 和负ε Nd( t) 值（-11.7 到 -9.7）。里屯辉绿岩还显示出高 MgO (10.52–13.84 wt%)、Cr (956–1,162 ppm)、Co (26.5–65.6 ppm) 和 Ni (240–514 ppm) 含量和低 Rb/Sr 比 (0.01–0.03) ）。这些地球化学特征表明，利屯辉绿岩可能起源于以角闪石为基本相的富集岩石圈地幔源，并且利屯辉绿岩不受分步结晶和地壳污染的显着影响。结合鲁西地区基性岩（如蒙阴基性岩脉和济南辉长岩）的Sr-Nd同位素组成，我们的研究结果表明，鲁西地区下方岩石圈地幔可能在~144~124之间迅速富集Ma，是由下沉下地壳的序贯杂化引起的。