Two tales of the continental lithospheric mantle prior to the destruction of the North China Craton: Insights from Early Cretaceous mafic intrusions in western Shandong, East China

摘要

Weakened lithospheric zones such as the Dabie-Sulu orogenic belt and Tan-Lu fault zone played important roles in the destruction of the North China Craton(NCC) during the late Mesozoic.Early Cretaceous mafic intrusions in western Shandong, contemporary with extensive magmatism during the destruction of the NCC, delineate two spatially distinct mantle domains(EM1- and EM2-like) beneath the craton's interior and weakened lithospheric zones, respectively.The Jinan and Zouping gabbros from the craton interior(～128Ma) show fractionated LREE and nearly flat HREE patterns([La/Yb] _N=2.94-8.95;[Dy/Yb] _N=1.23-1.69) with notable negative Ta, Nb and Ti anomalies.They have strong negative ε _(Nd)(t)(-15.7 to -7.1), low initial ~(87)Sr/ ~(86)Sr(0.7039-0.7060) and negative zircon ε _(Hf)(t) of -20.0 to -6.2.These "crustal fingerprints" cannot be explained by crustal contamination, but were likely derived from a hybrid mantle source.Crustal delamination or detachment during the Early Paleoproterozoic might be responsible for the involvement of Early Precambrian crustal materials in the Mesozoic mantle source beneath the southeastern NCC.In comparison, the Early Cretaceous mafic igneous rocks from regions(e.g., Yinan, Mengyin and Fangcheng) adjacent to the Dabie-Sulu orogenic belt and Tan-Lu fault zone have higher ~(87)Sr/ ~(86)Sr ratios(0.7059-0.7119), suggesting modification of the lithospheric mantle by melts/fluids derived from the Yangtze crust.The Mesozoic crustal delamination may have triggered the destruction of the lithospheric root beneath the Dabie-Sulu orogenic belt, whereas the lithospheric thinning beneath the interior of the southeastern NCC is attributed to the thermo-mechanical erosion by lateral convective asthenosphere.