鲁西早白垩世基性侵入岩的锆石Hf同位素组成变化及其成因

鲁西北部地区的淄博和临朐辉长闪长岩的锆石原位U-Pb定年分析显示,它们分别形成于128±2Ma和132±1Ma,与鲁西早白垩世大规模岩浆活动时间一致,是华北克拉通岩石圈减薄过程的岩浆活动产物。与鲁西北部同时期的济南、邹平辉长岩相比,淄博和临朐辉长闪长岩的锆石εHf(t)值(分别为-5.1～-2.4和-2.4～+3.2)明显较高,并具有相对年轻的亏损地幔Hf模式年龄TDM(分别为876～984Ma和639～867Ma),对应于相对高的全岩εNd(t)值,指示其岩浆源区有更大比例的软流圈地幔物质贡献。鲁西北部地区的早白垩世基性侵入岩的岩浆源区以华北克拉通内部的古老富集岩石圈地幔为主,从华北克拉通内部往郯庐断裂带锆石εHf(t)值显示出升高趋势,表明软流圈地幔物质的参与比例增大。郯庐断裂带是导致鲁西地区早白垩世基性岩浆活动时空不均一性的重要岩石圈薄弱带。

Spatial Variation of Zircon Hf Isotopes for the Early Cretaceous Mafic Intrusions in Western Shandong and its Genesis

The in-situ zircon U-Pb dating revealed that the gabbro-diorites from Zibo and Linqu in Northwestern Shandong were formed at 128±2 Ma and 132±1 Ma,respectively.They are contemporary with the extensive Early Cretaceous magmatism in Western Shandong as results of the lithospheric thinning underneath the North China Craton(NCC).In comparison with the contemporaneous Jinan and Zouping gabbros,the Zibo and Linqu gabbro-diorites have notable higher zircon ε Hf(t)(-5.9～-2.5 and-2.5～+3.2,respectively) and younger zircon Hf model ages(876～1003 Ma and 639～867 Ma,respectively),suggesting a large contribution of the asthenosphere to the magmatism at Zibo and Linqu areas.Overall,the source of the Early Cretaceous mafic intrusions in the north of Western Shandong was dominantly old lithospheric mantle of the craton's interior.From the NCC's interior to the Tan-Lu fault,the zircon ε Hf(t) values of the Early Cretaceous mafic intrusions change from strong negative to less negative or slightly positive,indicating the increased participation of asthenosphere for the magmatism.The Tan-Lu fault should have been an important weaken lithospheric zone responsible for the spatial and temporal heterogeneous of the Early Cretaceous mafic magmatism in Western Shandong.